21. But for + n. / pron., sb. / sth. would (not) have done…..要不是…….,某人早就……(表示虚拟语气)=If it had not been for…..,……./If there had not been ……..
　　22. It won(’t) be long before +从句(从句中用一般现在时)不久/很久就要…….
　　It was (not) long before+从句(从句中用一般过去时)不久/很久才……..
　　23. Those who………….(从句及主句中谓语动词用复数形式).
　　Anyone who…………= Whoever………..(从句及主句中谓语动词用单数形式)
　　24.…….主句(一般现在时或过去时)…...when从句….(might/ should do 或might / should have done) 表示”对比”,意思为 “本该……(可)而却”,主句中为陈述语气,从句里为虚拟语气
　　Eg: Why are you here when you should be in school?你本该上学的怎么在这儿?
　　He stopped trying when he might have succeeded .本该已成功了他却停止努力了.
　　25. There is ./ Sb. have no doubt that………(同位语从句,that不可省略) 毫无疑问……
　　There is / Sb. have some doubt whether……..(同位语从句不可用if)不确定…是否…
　　Sb. Doubt if / whether……. 某人怀疑是否……
　　Sb. don’t doubt that……… 某人不怀疑……
　　26.immediately / directly / instantly / the moment +从句
　　on / upon + n. / doing
　　No sooner had sb. done than …….(过去时)
　　Hardly had sb. done when……..(过去时)
　　注意：这几个结构都表示“一…….就”;
　　27. every time / each time / the last time / the first time / next time +从句(名词性短语引导一个时间状语句)
　　anywhere / everywhere +从句(相当于wherever引导的地点状语从句)
　　Eg: You can go anywhere you like.
　　Next time you come, please bring your son along.
　　28.Ifonly / I wish +从句(用过去类时态) 表示虚拟语气, “要是…….就好了” “但愿……就好了!”
　　29.Considering+ n. 或 pron. 或 that从句 / Seeing that……….考虑到/鉴于…….
　　Given + n. / pron.作状语,表示 “在有……的情况下” “如果有” “假定”,有时也表示”考虑到”
　　Eg: Seeing (that) he refused to help us, there is no reason why we should help him now.
　　Given good health, I hope to finish the work this year.
　　Given their inexperience / that they are inexperienced, they’vedone a good job.
　　30.Therewas a time when…….曾经有那么一度……….
　　31.otherthan与no, not, none等否定词连用,表示肯定意思,如:
　　Eg: It was none other than Mr. Smith.这正是Smith先生.
　　32. Not until…….did / do/ does / will sb. do……
　　It was / is not until ……that sb………
　　33.It’s(un) like sb. to do / to have done……做某事很像某人/ 做某事可不像某人
　　34.Itremains to be seen Wh--words ……..是否…….还有待于看.(不用that, if作连接词)
　　35.Itonly remains for sb. to do……剩下的只是要某人做某事.
　　Eg: We’ve got everything ready. It only remains for you to come to dinner.
　　36.Onemoment……., and now………刚才一会儿还在做……而现在却……..
　　37.Notall / both / everyone………表示部分否定
　　38. Such is / are……..这(些)就是…….(谓语动词单复数由后面名词决定)
　　39.I’d rather (not) do / have done……我宁愿…..
　　I’d rather +从句(从句中用过去时或过去完成时)
　　40. It’s important / necessary / strange / surprising….+that……(用陈述语气或should do)
　　41. I like / hate / appreciate it that / when等从句 (it表示后面从句的这种情况)
　　Eg: I appreciate it if you will give me a hand.
　　42. By the time +从句(一般现在时/过去时)，主句(将来完成时/过去完成时)
　　43……….,as is often the case with sb. / as is usual with sb.(as引导非限制性定语从句)
　　44 in case / lest / for fear that…….(从句中用陈述语气或shoulddo)
　　45.While置于句首可表示As long as 或 Although
　　Eg: While there is life there is hope.
　　While I admit his good points, I can see his bad ones.
　　46. cannot ( never) ……too +adj. (adv. ) / adj. (adv.) + enough “越……越好”“非常”
　　too + adj. ( anxious / eager / willing / ready / glad等)+todo….表示肯定意思
　　Eg: I can’t thank you enough.我非常感激你.
　　He was too glad to see his father.=He was very glad to see his father.
　　47. not /never等表示否定的词与比较级连用表示最高级，如：
　　Eg:-----Do you agree with his suggestion?
　　-------I can’t agree more.
　　48. What if……..要是…….怎么办?
　　Eg: What if he doesn’t’t come tomorrow?
　　49. more……..than与其…….不如……..
　　Eg: He is more nervous than frightened.
　　50. It is/ has been +一段时间+since从句(从句中如为延续性动词,则实际表示的意思相反)
　　Eg: It is two years since he drank.他不喝酒已两年了.