请教一个关于定语从句that省略的问题--OG-69

69.
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

最终答案选E，其他解释我觉得都没有问题，只是关于D选项的解释：“that would have to be repeated in the clause that North Americans are exposed to”

为什么that一定要重复出来呢？我记得定语从句中的引导词如果是做“宾语，是可以省略的”

我理解是这样的:

D中的that...and that...是并列的定语从句,第一个定语从句中,因为that做从句的主语,所以that不能省,第2个定语从句中的that在从句中做宾语按语法讲可以省,但为了与第1个定语从句平行,所以也应该保留.

在单一的定语从句中,修饰成分紧邻被修饰语,如果引导词that在从句做宾语是可以省略的.

concluded that many of the dioxins that are currently uncontrolled and North Americans are exposed to come from the incineration of wastes.

如果这样，句子意思不对，会变成dioxins and NA are exposed to come from