从属连词加动词ing形式的造句

如:He didn't go to bed until his mother came back.由since,for,by,before, 来引导的时间状语从句。since 引导的时间状语是动作的开始时间，如:I have studied English since 1990.而by引导的时间状语通常是动作的结束时间，如：I had learned 25 English songs by the end of last term.