og 243 (sc菜鸟里的编号）

243. Some scientists have been critical of the laboratory tests conducted by the Federal Drug Administration on the grounds that the amounts of suspected carcinogens fed to animals far exceeds those that humans could consume.

(A)   far exceeds those that humans could consume

(B)   exceeds by far those humans can consume

(C)   far exceeds those humans are able to consume

(D)   exceed by far those able to be consumed
                    by humans

(E)    far exceed those that humans could consume

Choices B and C omit the conjunction that _an omission that is grammatically acceptable, but in the case of this sentence diminishes clarity.

有哪位NN能告诉我为什么用了that就会更清楚了呢？结构是什么呢