must的过去式和过去分词形式

You've been a great help, I must say.

依我看，你真是帮了个大忙啊。

I must go to the bank and get some money.

我得上银行取点儿钱。

He must be 70 if he's a day!

他至少70岁了！

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。