我认为你应该看医生。

I think you ___should see a doctor.

如果你对他感到恼火，你应该告诉他。

If you're annoyed with him, you ___should tell him.

如果你要去纽卡斯尔，你应该在彼得伯勒换乘火车。

You ___should change trains at Peterborough if you're going to Newcastle.