princess

我想A和D的区别就在于限定性和非限定性关系从句。限定性定语从句限制了它所修饰的名词，而非限定性关系从句仅对名词进行补充说明，对名词不起限制作用。
本题应该用非限定性关系从句，因为省略从句，句子的含义仍然是完整的，所以选A

给个例子吧，理解起来方便一点：
Where's the money that I lent you?
He lent me 1000 dollars, which was exactly the amount I need.

princess

mihu, here's an example from OG:

258. The British sociologist and activist Barbara Wootton once noted as a humorous example of income maldistribution that the elephant that gave rides to children at the Whipsnade Zoo was earning annually exactly what she then earned as director of adult education for London.
(A) that the elephant that gave rides to children at the Whipsnade Zoo was earning
(B) that the elephant, giving rides to children at the Whipsnade Zoo, had been earning
(C) that there was an elephant giving rides to children at the Whipsnade Zoo, and it earned
(D) the elephant that gave rides to children at the Whipsnade Zoo and was earning
(E) the elephant giving rides to children at the Whipsnade Zoo and that it earned

此题答案是A,A是限定性定语从句。
而对于B，OG上有这样的解释：
In B, the structure of “noted... that the elephant, giving rides ..., had been earning” falsely implies that the reader already knows about the elephant--that is, that the existence of this particular elephant is not new information. 我觉得可以把分词短语giving。。。看成是非限定性的修饰成分，如果这儿用which gave rides...,应该也是错的。

不知道我说清楚了没有：）