Passage Reference: Almost all the energy that living things make use of comes in the beginning from the sun. The chief exception is the gravitational pull of the earth itself, and of the moon upon the waters of the earth. The sun gives out enormous quantities of energy in the form of radiation - rays of light and other forms of energy.

Tips: If a paragraph repeats one idea many times, that idea is usually the heading.

Why the other options are wrong:

• Energy From Food: Food is not discussed here. That comes later with plants and animals. This is a wrong section trap.
• Other Forms of energy: The paragraph does not list different types of energy. It explains one main source. This is a context shift trap.

Key Vocabulary:

• radiation = energy sent out as rays
• gravitational pull = force of attraction

Question Focus: Main idea - how food provides energy and its link to the sun

Passage Reference: . Green plants have the power, through the process called photosynthesis, to change the energy of sunlight into chemical energy. This is stored in the plant in the form of organic molecules. Some of the plants are eaten and the stored energy used by herbivorous animals - or by human beings. Human beings are omnivorous, that is their food and therefore, their energy can come from either plant or animal sources. But that energy originated in the sun.

Why this is correct: The paragraph explains how plants store energy and how animals and humans get energy by eating food. The focus is clearly food as an energy source.

Tips: If eating, plants, animals, or food are central, look for a heading about food energy.

Why the other options are wrong:

• Energy from the sun: The sun is mentioned, but only to explain where food energy comes from. This is an example-as-main-idea trap.
• Fossil fuels: No fossil fuels are discussed here. This is a wrong section trap.

Key Vocabulary:

• photosynthesis = making food using sunlight
• omnivorous = eating plants and animals

Question Focus: Main idea - fossil fuels as another form of solar energy

Passage Reference: C. To satisfy human needs, other kinds of energy are needed - mechanical, driving and heating. The energy for heating, or for driving heat engines, usually comes from a fuel and most fuels were once living things. Fuel obtained in this way, with the exception of wood and other fresh organic matter, is called fossil fuel and includes oil, natural gas and coal. All of these are the very ancient buried remains of animal or plant life. They are finite and the processes by which they were made are not repeatable. They are yet another form of solar or sun energy.

Why this is correct: This paragraph explains what fossil fuels are, where they come from, and why they are limited. That is the clear central topic.

Tips: Names like oil, coal, and gas almost always point to fossil fuels.

Why the other options are wrong:

• Other Forms of energy: The paragraph focuses on one specific type, not many kinds. This is a partial truth trap.
• Energy from the sun: The sun is mentioned only as background. This is an example-as-main-idea trap.

Key Vocabulary:

• finite = limited
• organic matter = material from living things

Question Focus: Main idea - introducing and contrasting fission and fusion

Passage Reference: D. The energy given out by the sun is created by the process known as nuclear fusion. Fusion means 'joining together'. The opposite process is nuclear fission, meaning 'splitting apart" or 'dividing'. If either fission or fusion takes place quickly, the result is a great and sudden release of energy - an explosion, in fact. Both kinds of nuclear event can be created on earth but so far the only one that can be slowed down and controlled is fission.

Why this is correct: The paragraph defines both fusion and fission and explains the difference between them. It introduces both processes together.

Tips: When a paragraph compares two ideas, the heading usually names both.

Why the other options are wrong:

• Nuclear Fusion: Fusion is only half of the paragraph. Fission is equally important. This is a partial truth trap.
• The nuclear Fission chain reaction: Chain reactions are explained later, not here. This is a wrong section trap.

Key Vocabulary:

• fusion = joining
• fission = splitting

Question Focus: Main idea - how a fission chain reaction works

Passage Reference: E. Nuclear fission is the splitting of the nucleus of an atom. Only a few elements are suitable for use in this way, the most important ones being Uranium-235, Uranium-233 and Plutonium-239. When a nucleus of one of these elements is struck by a free neutron, it breaks down into two lighter nuclei which fly apart at high speed, colliding with surrounding atoms. Their kinetic energy is converted into heat energy. At the same time, two or three free neutrons are released and one of them enters the nucleus of a neighbouring atom, causing fission to occur again; and so on. The reaction spreads very quickly, with more and more heat energy released. This is called a 'chain'' reaction because the splitting of each nucleus is linked to another, and another and another.

Why this is correct: The paragraph describes step by step how fission continues again and again. The repeated linking is the key idea.

Tips: If a process is explained step by step, the heading often names that process.

Why the other options are wrong:

• Fission and Fusion: Fusion is not discussed here. This is a context shift trap.
• Uncontrolled and moderated nuclear reactions: Control is explained later, not in this paragraph. This is a wrong section trap.

Key Vocabulary:

• neutron = small particle in an atom
• kinetic energy = energy of movement

Question Focus: Main idea - difference between bomb and reactor fission

Passage Reference: r. F. If this reaction takes place in an atomic bomb, where nothing is done to slow it down, the result is a violent explosion that can destroy a town in a few seconds. Fission can also, however, take place within a construction called a nuclear reactor, or atomic pile. Here the highly fissile material (U-235, U-233, Pu-239) is surrounded by a substance that is non-fissile, for instance graphite. This material is called a moderator. The neutrons lose some of their energy and speed through colliding with the atoms of the moderator. Energy - heat energy - is still created on an enormous scale, but no expansion takes place. The moderator has another function: by slowing down the speed of the free neutrons, it makes it more likely that one of them will collide with the nucleus of a neighbouring atom to continue the chain reaction.

Why this is correct: The paragraph contrasts uncontrolled reactions in bombs with controlled reactions in reactors. Control is the main theme.

Tips: Look for contrast words like bomb versus reactor to spot comparison headings.

Why the other options are wrong:

• The nuclear Fission chain reaction: The chain reaction is assumed, not explained again. This is an example-as-main-idea trap.
• The advantages of nuclear energy: Advantages are discussed later. This is a wrong section trap.

Key Vocabulary:

• moderator = material that slows neutrons
• reactor = controlled nuclear system

Question Focus: Main idea - benefits of nuclear power compared to others

Passage Reference: on. G. The chief advantage of nuclear energy is that it does not depend on any local factors. A nuclear reactor, unlike an oil-well or a coal mine, does not have to be sited on top of a fossil-fuel source; unlike the solar energy unit, it does not have to go out of production when the sun is not shining; unlike hydroelectric power, it does not depend on a large flow of water which may be reduced during some seasons of the year. With an atomic power station, the only limiting factor is that of safety.

Why this is correct: The paragraph lists several benefits of nuclear energy compared to oil, solar, and water power.

Tips: Words like advantage, benefit, unlike usually signal a positive comparison.

Why the other options are wrong:

• Other Forms of energy: Other energy types are mentioned only for comparison. This is an example-as-main-idea trap.
• Dangers OF nuclear contamination: Safety is mentioned briefly, but dangers are not explained. This is a partial truth trap.

Key Vocabulary:

• sited = placed
• limiting factor = main restriction

Question Focus: Main idea - fusion process and why it cannot yet be controlled

Passage Reference: ety. H. In the opposite process, nuclear fusion, two nuclei come together to form a new nucleus of a different kind and this process also releases energy on an enormous scale. Fusion can only occur under conditions of very great heat - at least 50,000,000 degrees Celsius. (The temperature at the centre of the sun is estimated as 130,000,000 degrees Celsius.) A fusion reaction on earth has already been created - the hydrogen bomb. This is an uncontrolled reaction. It is not yet possible to produce a controlled fusion reaction that can be used for the production of useful energy.

Why this is correct: The paragraph focuses only on fusion, explaining how it works and why it is not yet usable.

Tips: If a paragraph focuses on one process only, choose the most specific heading.

Why the other options are wrong:

• Fission and Fusion: Fission is not discussed here. This is a context shift trap.
• Uncontrolled and moderated nuclear reactions: Control is mentioned, but only for fusion, not both types. This is a partial truth trap.

Key Vocabulary:

• fusion = joining nuclei
• uncontrolled = not managed

Question Focus: Main idea - overall summary using a metaphor

Passage Reference: ergy. I. Nuclear energy can be thought of as a kind of square. Three of the quarters of the square are known and used, but the fourth cannot y

Why this is correct: This short paragraph uses one clear metaphor to summarise nuclear energy knowledge.

Tips: Very short paragraphs often summarise, not explain details.

Why the other options are wrong:

• The advantages of nuclear energy: Advantages are not listed here. This is a wrong section trap.
• Nuclear Fusion: Fusion is not named directly. This is a context shift trap.

Key Vocabulary:

• metaphor = symbolic comparison
• quarter = one fourth

General Tips:

• Read all headings first and underline key words before matching.
• Match the MAIN IDEA, not a single word that looks similar.
• Headings usually follow paragraph order from top to bottom.
• If two headings seem possible, choose the one that covers more of the paragraph.
• Do not reuse a heading once it is matched.