Meaning: 'Major' means significant or important, indicating that the Andes are a key contributor to diversity.

Wrong options:

• reservoirs: 'Reservoirs' is a plural noun that refers to storage places, which does not fit as it does not describe the source of diversity.
• superb: 'Superb' is an adjective meaning excellent, which does not appropriately describe the source in this context.
• enlarge: 'Enlarge' is a verb that means to make larger, which does not fit grammatically as it does not modify 'source'.
• start: 'Start' is a verb that indicates the beginning of something, which does not relate to the context of describing a source of diversity.
• counter: 'Counter' is a verb that means to oppose, which does not fit as it does not describe the source of diversity.
• tropical: 'Tropical' is an adjective that describes a type of climate or region, which does not fit as it does not describe the source.

Correct answer: reservoirs

Explanation: The term 'reservoirs' is a plural noun that refers to large storage areas, in this case, for biological diversity. It fits grammatically as it serves as the object of the preposition 'of' and aligns with the context of discussing biodiversity.

Meaning: 'Reservoirs' refers to places where something is stored, here indicating areas rich in biological diversity.

Wrong options:

• major: 'Major' is an adjective that describes significance, which does not fit as it does not refer to a type of area for diversity.
• superb: 'Superb' is an adjective meaning excellent, which does not fit as it does not describe a type of area for diversity.
• enlarge: 'Enlarge' is a verb that means to make larger, which does not fit grammatically as it does not refer to a type of area.
• start: 'Start' is a verb that indicates the beginning of something, which does not relate to the context of describing areas of diversity.
• counter: 'Counter' is a verb that means to oppose, which does not fit as it does not describe a type of area for diversity.
• tropical: 'Tropical' is an adjective that describes a type of climate or region, which does not fit as it does not refer to a type of area.

Correct answer: counter

Explanation: The word 'counter' serves as a verb that indicates opposition to an idea. It fits grammatically as it describes the action of the finding in relation to the prevailing idea about Amazonian diversity.

Meaning: 'Counter' means to oppose or contradict, indicating that the finding challenges existing beliefs about biodiversity.

Wrong options:

• major: 'Major' is an adjective that describes significance, which does not fit as it does not indicate an action of opposition.
• reservoirs: 'Reservoirs' is a plural noun that refers to storage areas, which does not fit as it does not indicate an action.
• superb: 'Superb' is an adjective meaning excellent, which does not fit as it does not indicate an action of opposition.
• enlarge: 'Enlarge' is a verb that means to make larger, which does not fit grammatically as it does not indicate an action of opposition.
• start: 'Start' is a verb that indicates the beginning of something, which does not relate to the context of opposing an idea.
• tropical: 'Tropical' is an adjective that describes a type of climate or region, which does not fit as it does not indicate an action.

Correct answer: tropical

Explanation: The term 'tropical' is an adjective that describes the type of forest being referred to. It fits grammatically as it modifies the noun 'forest' and aligns with the context of discussing the Amazon's biodiversity.

Meaning: 'Tropical' refers to regions of the Earth that are warm and humid, typically near the equator, indicating the type of forest in question.

Wrong options:

• major: 'Major' is an adjective that describes significance, which does not fit as it does not describe the type of forest.
• reservoirs: 'Reservoirs' is a plural noun that refers to storage areas, which does not fit as it does not describe a type of forest.
• superb: 'Superb' is an adjective meaning excellent, which does not fit as it does not describe a type of forest.
• enlarge: 'Enlarge' is a verb that means to make larger, which does not fit grammatically as it does not modify 'forest'.
• start: 'Start' is a verb that indicates the beginning of something, which does not relate to the context of describing a type of forest.
• counter: 'Counter' is a verb that means to oppose, which does not fit as it does not describe a type of forest.

Correct answer: basin

Explanation: The word 'basin' is a noun that refers to a natural depression in the Earth's surface where water collects, in this case, referring to the Amazon basin. It fits grammatically as it serves as the object of the preposition 'in' and aligns with the context of discussing biodiversity.

Meaning: 'Basin' refers to a geographical area that collects water, here indicating the region rich in biodiversity.

Wrong options:

• major: 'Major' is an adjective that describes significance, which does not fit as it does not refer to a geographical area.
• reservoirs: 'Reservoirs' is a plural noun that refers to storage areas, which does not fit as it does not refer to a geographical area.
• superb: 'Superb' is an adjective meaning excellent, which does not fit as it does not refer to a geographical area.
• enlarge: 'Enlarge' is a verb that means to make larger, which does not fit grammatically as it does not refer to a geographical area.
• start: 'Start' is a verb that indicates the beginning of something, which does not relate to the context of describing a geographical area.
• counter: 'Counter' is a verb that means to oppose, which does not fit as it does not refer to a geographical area.