A.I. Explanation:

Correct answer: characteristic

Explanation: The word 'characteristic' fits grammatically as a noun that describes a defining feature shared by the poorest nations, aligning contextually with the discussion of aridity as a common trait.

Meaning: 'Characteristic' refers to a distinguishing quality or trait that defines something, in this case, the shared feature of aridity among poor nations.

Wrong options:

• economy: 'Economy' refers to the system of production and consumption in a country, which does not fit the context of describing a shared feature.
• rhythm: 'Rhythm' pertains to a pattern of sounds or movements, which is irrelevant in the context of discussing water scarcity and poverty.
• sequence: 'Sequence' implies an order or arrangement, which does not appropriately describe a defining feature related to aridity.

Correct answer: piece

Explanation: The word 'piece' is a noun that fits grammatically and contextually, indicating a missing part of the puzzle regarding economic disparity, which aligns with the metaphor used.

Meaning: 'Piece' refers to a part of a whole, suggesting that limited water availability could be an essential component in understanding economic disparity.

Wrong options:

• impact: 'Impact' refers to the effect or influence of one thing on another, which does not fit as a missing part in the context of a puzzle.
• import: 'Import' refers to goods brought into a country, which is unrelated to the metaphor of a puzzle piece in this context.
• window: 'Window' typically refers to an opening or opportunity, which does not convey the idea of a missing part of a complex puzzle.

Correct answer: exceeding

Explanation: The word 'exceeding' is a present participle that fits grammatically and contextually, indicating countries that surpass the specified rainfall threshold, aligning with the discussion of economic prosperity.

Meaning: 'Exceeding' means going beyond a certain limit, in this case, referring to countries that receive more than 500 millimeters of rainfall.

Wrong options:

• persisting: 'Persisting' implies continuing despite difficulties, which does not fit the context of surpassing a rainfall threshold.
• switching: 'Switching' suggests changing from one state to another, which is irrelevant in the context of rainfall and economic prosperity.
• scoring: 'Scoring' typically refers to achieving points or marks, which does not apply to the context of rainfall amounts.

Correct answer: through which

Explanation: The phrase 'through which' fits grammatically and contextually, indicating the means by which aridity affects economic growth, aligning with the structure of the sentence.

Meaning: 'Through which' indicates the method or process by which something occurs, in this case, how aridity hampers economic growth.

Wrong options:

• by them: 'By them' is vague and does not clearly indicate the means of how aridity impacts economic growth.
• in that: 'In that' suggests a reason but does not fit the grammatical structure needed to connect the mechanisms to aridity.
• of those: 'Of those' is unclear and does not provide the necessary connection between aridity and economic growth.

Correct answer: grounds

Explanation: The word 'grounds' fits grammatically and contextually as a noun indicating a place where something occurs, specifically referring to stagnant water bodies as breeding areas for pathogens.

Meaning: 'Grounds' refers to areas or locations, in this case, where stagnant water becomes a breeding site for disease-causing organisms.

Wrong options:

• targets: 'Targets' implies something aimed at or focused on, which does not fit the context of breeding areas for pathogens.
• equations: 'Equations' refer to mathematical statements, which are irrelevant in the context of discussing disease and water.
• seas: 'Seas' refers to large bodies of saltwater, which does not accurately describe the breeding sites for pathogens in stagnant water.