should better not后面加什么

例句：

When should you prune apple trees?

苹果树应该什么时候剪枝？

Should police officers carry guns ?

警察应该佩枪吗？

No income should remain undeclared.

一切收入均应申报。

The selectors should resign en bloc.

这些选择者应该集体辞职。

You should have seen it!

你应该看见的！