Sally found what they said was right.

问题描述:

Sally found what they said was right.
为什么用what 而不用that

what引导的是一个宾语从句,what they said was right是这个句子的宾语,而what又代指they说的什么,是said的宾语.如果用that的话,就会发现said后面是没有宾语they said—— 句子成分就不完整了