当然可以啊,
定语从句的引导词与先行词是复数还是单数无关的,
最重要是先行词在从句中所作成分,
还有就是先行词如果在从句做主语时,从句的谓语动词的数需要与先行词一致。
例如:
I like the books that were bought yesterday.
I like the food that is cooked by my mother.
答案都是可以的。定语从句的关系代词并不分单复数。只是分是人或是物,which用于指物(或在非限定定于从句中指代前面的词组或一句话),that即可指人也可指物,但不用于非限定定于从句中
可以
只能用whoThosewhobetrayfriendscannotbeforgiven.