Read the following passage.
A. Zebra mussels are small freshwater mollusks, usually 2 to 2.5 centimetres long, with zigzag patterns of black or brown on white and yellow. They come from the region around the Black and Caspian seas in southeastern Europe. In the late 1980s they entered the Great Lakes in ballast water discharged from ships, and the first established population was discovered in 1988 in Lake St. Clair, which connects to Lake Erie and Lake Huron. Scientists have deduced that the likely source was a single cargo ship travelling from the north shore of the Black Sea, which released larvae during its ballast exchange.
B. From there the mussels spread quickly across the Great Lakes and later through much of eastern Canada and the United States. They breed fast, since a female can release up to one million eggs in each breeding season. The larvae, called veligers, are microscopic and swim freely for up to a month, carried by currents until they settle on a solid surface. Adults then fix themselves to rocks, docks, boats and plants with strong threads, sometimes at densities of more than 700,000 per square metre. Out of water they can live for up to 18 days in high humidity, which lets them be carried over land on boats.
C. Each mussel feeds by filtering water, and a large population can quickly clear the water of almost all floating particles. In Lake Erie, transparency increased by 100 per cent during the first years of the invasion. The filtering removes plankton that native species feed on, which can shift local food webs. Zebra mussels also attach to native mussels, many of which are species at risk, and can suffocate them. In Canada they do millions of dollars in damage each year by clogging the intakes of power stations and water treatment plants.
D. Once established, a population is very hard to remove, so management focuses on prevention. Zebra mussels are one of six species prohibited under the federal Aquatic Invasive Species Regulations, so they cannot legally be imported into Canada. Since January 1, 2022, Ontario's Invasive Species Act has required boaters to clean plants and animals off their boats and to drain standing water before launching. Ships coming into the St. Lawrence Seaway from beyond the sea zone Canada controls are inspected before they enter the Great Lakes, to check that they have exchanged their ballast. Since these inspections began in 2006, no new non-native species attributed to ballast water has been reported in the Great Lakes.
E. Not given in any of the above paragraphs.
Decide which paragraph, A to D, has the information given in each statement below. Select E if the information is not given in any of the paragraphs.
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Correct Answer: C
Why this is correct: Paragraph C says zebra mussels attach to native mussels and can suffocate them. Attaching means fastening on, and suffocating kills the native mussel.
Passage Reference: Zebra mussels also attach to native mussels, many of which are species at risk, and can suffocate them.
Tips: More than one place says what the mussels fasten onto. Find the place where the other animal can die from it.
Why the other options are wrong:
- A: Paragraph A tells where the mussels came from and when they arrived, with no harm to other animals yet.
- B: Paragraph B lists rocks, docks, boats and plants as places adults cling to, but not other mussels, and nothing dies there.
- D: Paragraph D covers laws and inspections meant to stop the spread. It does not describe what happens to native mussels.
- E: The suffocation of native mussels by zebra mussels that attach to them is described in Paragraph C.
Correct Answer: A
Passage Reference: In the late 1980s they entered the Great Lakes in ballast water discharged from ships, and the first established population was discovered in 1988 in Lake St. Clair, which connects to Lake Erie and Lake Huron.
Why this is correct: Paragraph A says the first established population was discovered in 1988 in Lake St. Clair. An established population is one that has settled in to stay, which is a lasting group.
Tips: Lakes are named in several paragraphs. Find the one that says where the first population appeared.
Why the other options are wrong:
- B: Paragraph B follows the spread across the Great Lakes and beyond, but it names no first site.
- C: Paragraph C reports clearer water in Lake Erie, which is a later effect and a different lake.
- D: Look at paragraph D: it says established populations are hard to remove, yet it never says where the first one was found.
- E: Lake St. Clair, where the first established population turned up in 1988, is named in Paragraph A.
Correct Answer: C
Passage Reference: In Lake Erie, transparency increased by 100 per cent during the first years of the invasion.
Why this is correct: Paragraph C says that in Lake Erie, transparency increased by 100 per cent during the first years of the invasion. Transparency is how clear the water is, and a rise of 100 per cent means it doubled.
Tips: Find the lake where the water became clearer. Check how much clearer it got, and whether that means twice as clear.
Why the other options are wrong:
- A: Paragraph A mentions Lake Erie only as a lake joined to Lake St. Clair. It says nothing about clarity.
- B: In paragraph B, the writer describes how fast the mussels breed and spread, not how the water changed.
- D: In Paragraph D the focus is rules for boats and ships, and no change in water clarity is reported.
- E: The 100 per cent rise in transparency in Lake Erie appears in Paragraph C, where filtering is explained.
Correct Answer: E
Passage Reference: In the late 1980s they entered the Great Lakes in ballast water discharged from ships, and the first established population was discovered in 1988 in Lake St. Clair, which connects to Lake Erie and Lake Huron.
Why this is correct: Paragraph A says the first established population was discovered in 1988 in Lake St. Clair. It gives the year and the place, but it does not say who found the mussels.
Tips: The first paragraph says when and where. Check whether it also says who.
Why the other options are wrong:
- A: The discovery itself is reported in Paragraph A, with its year and lake, but the finders are never identified.
- B: The second paragraph explains breeding and larvae. No divers or researchers appear.
- C: Notice that paragraph C looks at clear water, native mussels and clogged intakes, not at the people who first saw the invaders.
- D: The fourth paragraph deals with regulations and ship checks, not with the first sighting.
Correct Answer: D
Passage Reference: Since January 1, 2022, Ontario's Invasive Species Act has required boaters to clean plants and animals off their boats and to drain standing water before launching.
Why this is correct: Look at paragraph D. Since January 1, 2022, Ontario's Invasive Species Act has required boaters to drain standing water from their boats before launching. A requirement in an act is a legal duty.
Tips: The second paragraph shows why boats matter. The legal duty itself is in a different paragraph.
Why the other options are wrong:
- A: The first paragraph speaks of ships releasing ballast water, not of ordinary boaters or any law for them.
- B: Look at paragraph B: it explains that mussels can ride on boats over land, but it states no rule for boat owners.
- C: Notice that paragraph C describes the harm mussels cause to lakes and pipes, with no duties for boaters.
- E: Ontario's Invasive Species Act, which makes boaters drain standing water, is set out in Paragraph D.
Correct Answer: E
Passage Reference: In Canada they do millions of dollars in damage each year by clogging the intakes of power stations and water treatment plants.
Why this is correct: The third paragraph says zebra mussels cause millions of dollars in damage in Canada every year. It does not compare that cost with the damage done by any other species.
Tips: The statement compares these mussels with every other invading species. Check whether any place makes that comparison.
Why the other options are wrong:
- A: The mussel and its arrival fill paragraph A, and no cost is given.
- B: In paragraph B, the writer gives large numbers for eggs and densities, but no ranking against other invaders.
- C: A yearly damage figure makes Paragraph C tempting, yet it never says this is more than for any other species.
- D: The fourth paragraph mentions other non-native species only to say no new ones arrived by ballast. It ranks none of them by damage.
Correct Answer: D
Passage Reference: Ships coming into the St. Lawrence Seaway from beyond the sea zone Canada controls are inspected before they enter the Great Lakes, to check that they have exchanged their ballast.
Why this is correct: The fourth paragraph talks about ships coming into the St. Lawrence Seaway from beyond the sea zone Canada controls. It says they are inspected before they enter the Great Lakes. Being inspected is being examined.
Tips: Ships and ballast come up more than once. Ask which paragraph describes someone checking ships before they come in.
Why the other options are wrong:
- A: Notice that paragraph A also involves a ship and its ballast, but that ship brought the mussels in. Nobody inspected it.
- B: In paragraph B, the writer says mussels travel on boats, not that ships are examined on arrival.
- C: Paragraph C deals with effects on water, native mussels and pipes. Ship checks do not appear.
- E: The inspection of ships from beyond the sea zone Canada controls before they enter the Great Lakes is in Paragraph D.
Correct Answer: B
Passage Reference: The larvae, called veligers, are microscopic and swim freely for up to a month, carried by currents until they settle on a solid surface.
Why this is correct: The second paragraph says the larvae, called veligers, swim freely for up to a month. Currents carry them until they settle on a solid surface. Up to a month means several weeks.
Tips: Young mussels come up in more than one place. Find the one that says how long they drift, and check that it fits 'weeks'.
Why the other options are wrong:
- A: Look at paragraph A: it says larvae were released from a ship, yet the length of their time adrift is left out.
- C: How adult mussels feed and harm other life is the topic of the third paragraph, not how the young live.
- D: Notice that paragraph D is about prevention rules and gives no details of the larval stage.
- E: How long the veligers swim before they settle, up to a month, is explained in Paragraph B.
Correct Answer: D
Passage Reference: Zebra mussels are one of six species prohibited under the federal Aquatic Invasive Species Regulations, so they cannot legally be imported into Canada.
Why this is correct: The fourth paragraph says zebra mussels are one of six prohibited species under the federal Aquatic Invasive Species Regulations. So they cannot be imported into Canada. Prohibited means banned by law.
Tips: Several places explain how the mussels travel. Ask which one is about what the law allows, not about how they arrived by chance.
Why the other options are wrong:
- A: Look at paragraph A: it shows how the mussels first came in by ship. No law against bringing them is mentioned.
- B: In paragraph B, the writer describes the spread across Canada and the United States, not a ban on imports.
- C: Notice that paragraph C gives the cost of the damage in Canada but names no law.
- E: The federal ban that stops zebra mussels from being imported into Canada is in Paragraph D.
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