（紧急求助）GMATpret test 2 一题请教，谢谢

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".

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

answer: D

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question:C是错在"that"的指代么？为什么不可以把that理解为中心词commitment呢？

正确答案中的had是个实义动词吧，难道不应该用did么？

谢谢~

up~

谢谢mydream1977。

从effectiveness来讲，less的确比smaller更加确切。

但是我对D中had的补出有些不解：

如果had是助动词，补全为had had，但是用过去完成时没有依据

如果had是实义动词，则有这种用法么？不应该补出did么？

或者这样说，选项只能选最好的，相较之下，D补出had 比B更加好吧。。

没有最好，只有更好。。。。

同意icerach的讲法, 选出最好的答案