GWD2－2，4答案到底是什么亚

D.

Keystone status appears to depend on          15

context, whether of particular geography or of such factors as community diversity              16

(for example, a reduction in species diversity may thrust more of the remaining species   17

into keystone roles) and length of species interaction (since newly arrived species           18

in particular may dramatically affect ecosystem).

GWD-2-4:

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 made by 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.

Question 2:

The primary purpose of the passage is to

A.      point out some of the differences between dominant and keystone species

B.      emphasize the complexity of the interactions that occur between two particular species

C.      detail the effect of a particular habitat on the role occupied by a certain keystone species

D.     illustrate the importance of community diversity for the perpetuation of an ecosystem

E.      explain some considerations involved in determining whether a species occupies a keystone role

为什么答案是D 而不是E