根据中文意思完成句子。（共10分，每小题2分）你看上去很累了。为什么不请人帮帮忙呢？
You look very tired. ______________ask someone for help?我认为你没有必要为那件事担心。
_______________you need to worry about that.你一到美国就给我打电话好吗？
Will you ring me up _________________?你最好不要让他抄你的作业。
___________________let him copy your homework. 必须采取措施阻止他花大量时间玩电子游戏。
Something must be done to________________.
为了安全起见，请不要到人群密集的地方． ．
To save people's lives，the doctors and scientists are risking their lives to do （医学的）research．
Our teachers often encourage us to face the difficulties （勇敢地） and try to overcome them．
When we are in danger， it's very important to make a good （决定）．
Make sure there are no （错误） in your test paper before handing it in．