Much more importantly, "smaller" vs. "less of a" is there just to distract you. You don't actually need it to solve the problem.
* You can eliminate a/b/c because the comparison has two possible meanings: (1) commitment to work vs. commitment to family, or (2) young people's commitment to work vs. their parents' and grandparents' commitment to work.
* You can eliminate E because "than" is there without "less".

为什么是HAD不是DID？就算是时态变换不也应该是DO换成DID吗？真的实在搞不懂GMAT的套路。。。

Much more importantly, "smaller" vs. "less of a" is there just to distract you. You don't actually need it to solve the problem.
* You can eliminate a/b/c because the comparison has two possible meanings: (1) commitment to work vs. commitment to family, or (2) young people's commitment to work vs. their parents' and grandparents' commitment to work.
* You can eliminate E because "than" is there without "less".

［比较问题］
如果比较两边时态相同的话，than后面的have确实是可以省略的，但是年轻人和父母爷爷奶奶比，平行过去肯定爸爸妈妈那个时候是过去的情况，所以had是需要补充出来的［时态变了］

要看是主语比较还是宾语比较吧？
如果their parents and grandparents是主语，可以省略had
如果their parents and grandparents是谓语，那么就是年轻人们对工作的commitment比对他们老爷子的commitment少 明显不对 AB就没了 CE是不是通过前面的smaller和lessening去掉？

lessen，v减轻，变少；lessening，n减轻

I eat less of these foods than I did ten years ago.
"”> I eat these foods in smaller servings. This doesn't mean that I eat fewer of them (= that I've cut any of them out of my diet).

I eat fewer of these foods than I did ten years ago.
"”> Ten years ago, I ate N of these foods, where 0 < N ≤ 10.
Now I eat M of them, where M < N.
This statement implies nothing about serving size

E选项里用了than，但是没有比较级

［比较问题］
如果比较两边时态相同的话，than后面的have确实是可以省略的，但是年轻人和父母爷爷奶奶比，平行过去肯定爸爸妈妈那个时候是过去的情况，所以had是需要补充出来的［时态变了］

c不对，是。。。have 。。。 than。。had。

mark

I eat less of these foods than I did ten years ago.
"”> I eat these foods in smaller servings. This doesn't mean that I eat fewer of them (= that I've cut any of them out of my diet).

I eat fewer of these foods than I did ten years ago.
"”> Ten years ago, I ate N of these foods, where 0 < N ≤ 10.
Now I eat M of them, where M < N.
This statement implies nothing about serving size.

"Less of a/an ___" doesn't refer to a literal quantity. It's an expression that means, roughly, "not as true" or "not having as much of the essence of a/an ____".
Since that's an awkward definition, here is an example:
My grandfather thought that crying made you less of a man. (i.e., like "less manly")

there is ambiguity if you eliminate the helping verb.
without the helping verb, there are two interpretations:
1: young people are less committed to work/career than WERE their parents/grandparents (the intended meaning)
2: young people are less committed to work/career than TO their parents/grandparents
you can't tell which of these is the correct meaning without the helping verb; therefore, the helping verb is necessary.

less=抽象，small+具象，同时谓语动词不能省略

句子的逻辑意思是“young people现在比他们parents and grandparents过去对work and career有更少的commitment”，即前后比较的对象是young people和parents and grandparents，而grandparents有commitment是在过去，因此两者的谓语动词需明确写出来，不能省略。
从比较对象出发，排除C；从比较的时态出发，排除A/B；
英语中smaller用于修饰具体的事物，less用于修饰抽象的事物。由此排除A/C；E：a lessening of 表示减少的，用在此不合理，排除E；D：less of “较少的”，可用于表示比较。

Option C is wrongly comparing young people with commitment, which is wrong.

had是因为改变了时态 所以要保留动词

v+ less of/more of + n. than..., 表示在更小程度上/更大程度上做某事，less of/more of是用来修饰动词的