[求助]OG 132(这问题没问过）

OG 132
132. 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

答案是E

The phrases equivalent to in A, the equivalent of in B, and equal to in C have too broad a range of meanings to be used precisely here: that is, they can suggest more than merely numerical equality. Also, as quantitative expressions, equiva­lent and equal often modify nouns referring to uncountable things, as in "an equivalent amount of resistance" or "a volume of water equal to Lake Michigan." To establish numerical comparability between groups with countable members, the phrase as many as is preferable. Choice D, however, uses this phrase improperly in comparing eight million people to enrollment, not to other people. The comparison in E, the best choice, is logical because people is understood as the subject of are enrolled.

想请问一下在D中，enrollment是注册人数的意思呀，为什么不能和前面的eight million people平行呢？谢谢

people vs. enrollment

人 和 注册人数（数字） 不平行的。