1.宾语是反身代词或相互代词时,谓语动词用主动,不能用被动
比如说They help each other.他们互相帮助.这时候句子就不能转换成被动语态
2.宾语是及物动词的同源宾语,不定时、动名词等谓语动词不用被动
比如说She dreamed a bad dream last night.这里后面的名词dream就是前面动词dreamed的同源宾语.
She likes to swim.不定式为动词宾语,不能转换成被动语态
同理She likes swimming.动名词做宾语,也是不可以的