You must signal which way you are going to turn.
你要朝哪个方向转，必须发出信号。
You're a great help, I must say!
我得说，你可没少帮忙！
There must be a way around the problem.
肯定有解决这个问题的办法。
The work must be completed within a certain time limit.
这项工作必须在一定期限内完成。
There is a growing realization that changes must be made.
越来越多的人认识到改革势在必行。