which后面加可数名词的单数和复数都可以

它可以翻译成：哪一个，也可以翻译成：哪一些比如：Which book do you want? 你想要哪一本书Which glasses do you want? 你想要（喜欢）哪些眼镜

如果which指代的先行词是物，根据物的性质，可以是单数，也可以是复数。

如：

She gave me a book， which is expensive.

She gave me some books， which are bought from a nearby bookshop.

但which指代的先行词也可能是前面整个一个句子，那个这个时候which后面的谓语动词只能用单数。

如：

She got an A in the exam， which was due to her diligence.