求助1道题，谢了啊~

zhoujoy

150.    (32705-!-item-!-188;#058&007266)
Hydrocarbons, with which fruit flies perfume themselves in species-specific blends, are known to be important in courtship, and apparently this assists flies that taste the hydrocarbons on prospective mates to distinguish their own species from that of others.
(A) and apparently this assists flies that taste the hydrocarbons on prospective mates to distinguish their own species from that of
(B) and apparently this assists flies when they taste the hydrocarbons on prospective mates in distinguishing their own species from those of
(C) which apparently assists flies that taste the hydrocarbons on prospective mates in being able to distinguish their own species from
(D) apparently assisting flies to taste the hydrocarbons on prospective mates to distinguish their own species from those of
(E) apparently assisting flies that taste the hydrocarbons on prospective mates in distinguishing their own species from
为什么不选D 呢？

cx_ding

those没有指代对象。