选A.
定语从句拿出来,调整一下,就是：the book's cover is red.
然后用whose 替代the book's ,表book 和 cover之间的所属关系.高手再问一题：____cleans the classroom should be praisedAThatBWho CTHe one whos D The students who选D。the students 作先行词，关系代词who 引导定语从句，连接主从，同时在从句中充当主语