should 的同义词为：
ought to, be supposed to,等
ought to一般用于阅读中，用法普遍
be supposed to 是比较正式的说法，书面语较多。
You ought to scrap the old bike and buy a new one.
你应该扔掉这辆旧自行车，买一辆新的。
I think I ought to get back to work.
我想我该回去工作了。
Perhaps we ought to have trusted people more
也许我们本当对人多一些信任的。
