OG13阅读114题，急求解答！！

Sophie92

114. The passage suggests which of the following about the identification of a species as a keystone species?
(A) Such an identification depends primarily on the
species' relationship to the dominant species.
(B) Such an identification can best be madeby
removing the species from a particular
ecosystem and observing changes that occur in
the ecosystem.
（C）Such an identification is likely to be less reliable
as an ecosystem becomes less diverse.
(D) Such an identification seems to depend on
various factors within the ecosystem.
(E) Such an identification can best be made by
observing predation behavior.
答案是D可以理解，但是C有什么错呢？文中明确提到“Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction (since newly arrived species in particular
may dramatically affect ecosystems).” 官方答案中提到difficulty，一点都不明白。。。哪位大神可以帮忙解答一下