結(jié)構(gòu)┱If I+should ...+祈使語氣

　　說明┱代替，增加了條件的不確定性。本句型常用在想禮貌地提出要求或建議，或者想圓通地告訴他人該做什么事的場合。用 should 起始句子即可不用 if 而表示條件。這種用法比較正式，常用于諸如公函之中，而不用于日常會話。

　　If you should see him, please give him my regards. 如果你見到他，請代我向他致意。

　　Should you see him, please give him my regards. 如果你見到他，請代我向他致意。

　　If you should happen to see him, please give him my regards.

　　如果你萬一見到他，請代我向他致意。

　　Should you happen to see him, please give him my regards.

　　如果你萬一見到他，請代我向他致意。

　　If you should write to her, send her my love. 如果你給她寫信，請代我向她問候。

　　Should you not wish our agent to call, please let us know.

　　你若不希望我們的代理人去造訪，請告之。

　　Should you be interested in our offer, please contact us.

　　你若對我們的報價感興趣，請與我們聯(lián)系。

　　If I should ..., I will ...

　　結(jié)構(gòu)┱If…should…，…would(will)/should(shall)等+原形動詞

　　說明┱這是表示與未來事實(shí)相反的假設(shè)，if 要用 should，譯成“萬一”。should可置于前，將 if 省略。的則視可能性做變化：若可能性低，則為過去式，若可能性高，則為現(xiàn)在式。should 可以提前，而將 if 省略。

　　If he should come, I would tell him the truth. 萬一他來，我會把真相告訴他。

　　If he should come, I will tell him the truth. 萬一他來，我一定會把真相告訴他。

　　Should the boy come again, I would throw him out. 要是那男孩在來，我就把他攆出去。

　　If it should rain, our plan would be spoiled. 萬一下雨，我們的計(jì)劃就泡湯了。

　　Should that be true, the contract would be canceled. 假如那是真的，合約就該取消。

　　Should another world war break out, what would become of human beings?

　　萬一另一次世界大戰(zhàn)爆發(fā)，人類將會發(fā)生什么事?

　　If I were to ..., I ...