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。IthinkIoughttogetbacktowork.我想我该回去工作了。Perhapsweoughttohavetrustedpeoplemore也许我们本当对人多一些信任的。