should和ought to的肯定、否定、疑问及其回答的形式

should和ought to都可译为“应该”，表示义务、责任或某个正确的行为。ought to比should语气略强些，多用于肯定句；疑问句与否定结构则多用should。should/ought to +have +过去分词表示过去应该做（或完成）而没有做的事。

He ought to have returned by now.

He had to change his plans, but he should be returning soon.