What he wanted to do was——A?——his hands of it.A.washB.to hav

A 这是因为what he wanted to do 是 what he wanted himself to do 的省略,是这句的主语从句.英语中规定句子中前面的从句有do 或者do 的某种形式,其后的不定时（短语）省to , 所以该句的表语（to） wash his hands 省去了to. 原句是What he wanted to do was （to）wash his hands of it.