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❓ 题目 According to the passage, which of the following statements about keystone species is TRUE?

A. A) Keystone species are always top predators in an ecosystem.
B. B) The effect of a keystone species is consistent across all habitats.
C. C) Keystone species can be identified based solely on their population size.
D. D) The concept of keystone species, while useful, has limitations due to context-dependence.

D) The concept of keystone species, while useful, has limitations due to context-dependence.

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Official TOEFL iBT Tests Vol.2