og34

34. 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

and D requires that before North Americans, to be grammatically complete.

为什么必须要加that才算是语法完整呢？

请nn指教！