请教prep一道~~~

25.
   (25704-!-item-!-188;#058&002607)

There is a widespread belief in the United States and Western Europe that young people have a smaller commitment to work and a career than their parents and grandparents and that the source of the change lies in the collapse of the "work ethic."

(A) a smaller commitment to work and a career than their parents and grandparents

(B) less of a commitment to work and a career than their parents and grandparents

(C) a smaller commitment to work and a career than that of their parents and grandparents

(D) less of a commitment to work and a career than their parents and grandparents had

(E) a lessening of the commitment to work and a career that their parents and grandparents had

这道题为什么后面their parents and grandparents had，而不是用have呢？这些动作不是都发生在现在么？

还有这里的less of a commitment 和 a smaller commitment有什么分别？

选C

that of is necessary to balance the comparison.

同意 可是我想问一下

less 不是用来修饰可数名词吗？ 为什么 less of a commitment 是可以接受的呢？

是因为是抽象名词吗？