虚拟语气（if）otherwise, without, or, but for, but that, given, provided, were it not for.（过去 would, should+have done, 现在/将来 would... do）
建议/命令/要求/主张/愿望+(should) do（比如：advise, suggest, order, recommend, propose, ask, command, insist, demand, desire, beg, require, urge, decide, determine）
This/ That/ It is the second time that...完成时
It is (about/ high) time (that)【到...的时候了，现在正是...的时候了】 过去式
no sooner... that; hardly...when前面用过去完成时，后面用一般过去时
was/were+ about to do...when/doing...when/on the point of doing...when when后面用一般过去时
