If industrial pollution continues to deplete the ozone layer, the resulting increase in ultraviolet radiation will endanger human health, causing a rise in the incidence of skin cancer and eye disease, and perhaps even threatening global ecological systems.
As written "
ultraviolet radiation will endanger human health, causing ... and perhaps even threatening ...", the sentence seems to present two HOW-aspects of the action "
will endanger human health".
It is not correct as "
causing a rise in the incidence of skin cancer and eye disease" definitely explains how UR causes bad things to human health, but "threatening global ecological systems" is not. This is an incident of forced parallelism, the second part does not explain the effect of UR of health rather completely different effect.
We need an answer choice that makes parallel another list: "will endanger" and "will threat".
Quote:
(A) and perhaps even threatening
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incorrect for the reason explained above Quote:
(B) and may even threaten
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correct Quote:
(C) and even a possible threat to
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"and" requires us to maintain parallelism: noun ("a possible threat") is not parallel to verb ("will endanger") Quote:
(D) as well as possibly threatening
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same as A Quote:
(E) as well as a possible threat to
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same as C