1. You took part in some volunteer activities during summer holidays, didn't you?你在暑假参加了一 些志愿者活动，是吗? 反意疑问句
e.g. It's a nice day, isn't it
Ann didn't use to live there, did she ?
2.Tohelpothersmakesushappy.帮助别人使我们快乐。
动词不定式做主语
e.g. To do sports every day is necessary.

3. Though I had no time to travel, I still felt very happy.
虽然我没有时间去旅行，但我仍然感到很开心。
though/although
even though/even if
虽然，尽管，即使让步状语从句通常不与but连用
e.g. Though/Although it was very late, the workers went on working.
虽然很晚了，但是工人们继续工作。
have (no) time to do sth.
有(没有)时间做某事
e.g. He was so busy that he had no time to have lunch.
他太忙了，没有时间吃午饭。