C,因为前面的主语是what he enjoys,这是一个从句作主语,而enjoy是从句的谓语动词,因此对于整个句子来说还缺少一个谓语,所以必须要有一个动词,只有C,is作谓语,后面是表语,再如
What he said is true排除其它三个选项的原因是？选A的话要去掉what，变成enjoy doing， 选B的话可以改成what he enjoys is to play ,用toplay 作表语，D是没法改的了，呵呵