Prep2012_Pack1_RC(题目版)(18)

dramatic increase in straying from damaged areas to more pristine streams results in

substantial gene flow, which can in turn lower the overall fitness of subsequent generations. PREP2012-Pack1-RC-008-01 VRC000460-01 Medium The primary purpose of the passage is to

A.

B. argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative correct a common misunderstanding about the behavior of salmon in response to

environmental degradation caused by human activity

C. compare the effects of human activity on salmon populations with the effects of natural

disturbances on salmon populations

D. differentiate the particular effects of various human activities on salmon habitats

E. describe how environmental degradation can cause changes in salmon populations that

extend beyond a numerical reduction

PREP2012-Pack1-RC-008-02 VRC000460-02 Hard

It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

A. pristine streams that are near polluted streams become polluted themselves

B. the particular adaptations of a polluted streams salmon population can be preserved

without dilution

C. the number of salmon in pristine habitats decreases relative to the number in polluted

streams

D. an environmentally degraded stream could be recolonized by new salmon populations

should the stream recover

E. the extinction of the salmon populations that spawn in polluted streams is accelerated PREP2012-Pack1-RC-008-03 VRC000460-03 Medium

According to the passage, human activity has had which of the following effects on salmon populations?

A.

B.

C.

D.

E. An increase in the size of salmon populations in some previously polluted rivers A in the number of salmon in some rivers A decrease in the number of straying salmon in some rivers A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams A decline in the vulnerability of some salmon populations to the effects of naturally

occurring habitat destruction

PREP2012-Pack1-RC-008-04 VRC000460-05 Hard

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