汉译英。初二，应该蛮简单的，不过我不知道

are supposed to 或 should have to .
不能用should或had better.因为三个空嘛,had better do sth,should do sth.
should have to do sth,表示你应当这样做,但却没有做 .这句话翻译过来就是:你本应该在你离开前说再见的.

You should go to say goodbye to him before you leave

are supposed to

had better to或者should

should或had better

had better to