92．According to a study by the Carnegie Foundation for the Advancement of Teaching，companies in the United States are providing job training and general education for nearly eight million people，about equivalent to the enrollment of the nation's four-year colleges and universities．

(A)  equivalent to the enrollment of

(B)  the equivalent of those enrolled in

(C)  equal to those who are enrolled in

(D)  as many as the enrollment of

(E)  as many as are enrolled in

why C is incorrect? 标准答案说什么equal修饰不可数名词，我觉得不是很有说服力

as many as 指得是个精确的数(number),会和这里的about产生矛盾.

equal指得是个数量(quantity),不会出现以上情况.

equavalent一般不用来指数量.

equal的意思更宽泛，不仅可以在数量上比较（时常比较不可数），还可以在其他方面比较．

所以to establish numerical comparability between groups with countable members, the phrase as many as is preferable

我觉的OG 说的满清楚的