80. A report by the American Academy for the Advancement of Science has concluded that much of the currently uncontrolled dioxins to which North Americans are exposed comes from the incineration of wastes.
(A) much of the currently uncontrolled dioxins to which North Americans are exposed comes
(B) much of the currently uncontrolled dioxins that North Americans are exposed to come
(C) much of the dioxins that are currently uncontrolled and that North Americans are exposed to comes
(D) many of the dioxins that are currently uncontrolled and North Americans are exposed
to come
(E) many of the currently uncontrolled dioxins to which North Americans are exposed come
答案容易选择，可对于OG中对于D选项的解释，不太理解，请NN解答，并且 that 在什么情况下可以省略？？谢谢大家~~~~
D That are is wordy; to maintain the parallel in this construction, that would have to be repeated in the clause that North Americans
are exposed to.
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