题目内容：

I don't know when l shall start the work.(用动词不定式改写）
I don't know when _____ _____ the work.

优质解答

动词不定式就是to do
do表示动词..
第一个格就用to
而原句的从句只有start是动词...
所以就用to start
I don't know when to start the work.