Meaning: Barriers are structures that prevent movement or flow, in this case, referring to how dams block or control river water.

Wrong options:

• deposits: Deposits refer to materials that are accumulated, which does not fit the context of what dams do to rivers.
• overlaps: Overlaps suggest a covering or extending over something, which does not accurately describe the function of dams.
• blizzards: Blizzards are severe snowstorms, which are unrelated to the function of dams in relation to rivers.

Correct answer: droughts

Explanation: The term 'droughts' is a plural noun that refers to prolonged periods of abnormally low rainfall, fitting contextually as it describes the negative impact that dams help mitigate.

Meaning: Droughts are extended dry periods where water supply is significantly reduced, often affecting agriculture and water availability.

Wrong options:

• barriers: Barriers, while relevant to the first blank, do not relate to the context of water scarcity and are not a type of weather phenomenon.
• occur: Occur is a verb that describes an event happening, which does not fit as it does not describe a type of water-related issue.
• blizzards: Blizzards are unrelated to the context of water scarcity and do not fit the discussion about water supply.

Correct answer: occur

Explanation: The verb 'occur' fits grammatically and contextually as it describes the potential event of flooding happening in the reservoir area behind the dam.

Meaning: Occur means to happen or take place, particularly in reference to events like flooding.

Wrong options:

• barriers: Barriers is a noun that does not fit in the context of describing an event happening.
• deposits: Deposits is a noun that refers to accumulated materials, which does not fit the context of flooding occurring.
• overlaps: Overlaps is a noun that suggests a covering, which does not describe an event like flooding.

Correct answer: collects

Explanation: The verb 'collects' fits grammatically as it describes the action of water gathering in the reservoir, aligning with the context of how dams function.

Meaning: Collects means to gather or accumulate, particularly in reference to water in the reservoir behind the dam.

Wrong options:

• barriers: Barriers is a noun that does not describe an action and does not fit in this context.
• deposits: Deposits is a noun that refers to accumulated materials, which does not fit the action of water gathering.
• overlaps: Overlaps is a noun that does not describe the action of water and is not relevant in this context.