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.
This question checks understanding for Countable verses Uncountable.(A) much of the currently uncontrolled dioxins to which North Americans are exposed comes-> currently uncontrolled is taking about the subject "dioxins" which is plural and countable. So, Much is incorrect.
(B) much of the currently uncontrolled dioxins that North Americans are exposed to come-> currently uncontrolled is taking about the subject "dioxins" which is plural and countable. So, Much is incorrect.
(C) much of the dioxins that are currently uncontrolled and that North Americans are exposed to comes-> currently uncontrolled is taking about the subject "dioxins" which is plural and countable. So, Much is incorrect.
(D) many of the dioxins that are currently uncontrolled and North Americans are exposed to come-> Many is better used here. But, "And North Americans are exposed to come" which is incorrect.
(E) many of the currently uncontrolled dioxins to which North Americans are exposed come-> Many is used. which is correct. To which is talking about Dioxins, makes sense.
So, I think E.