2010年12月大學(xué)英語四六級(jí)考試必備語法精要

　　6. 錯(cuò)綜時(shí)間條件句

　　條件從句表示的動(dòng)作和主句表示的動(dòng)作，有時(shí)發(fā)生的時(shí)間是不一致的.如從句是對(duì)過去情況的假設(shè)，而主句可能是對(duì)現(xiàn)在正在進(jìn)行情況的假設(shè)。 這種句子稱為錯(cuò)綜時(shí)間條件句.

　　If the weather had been more favourable, the crops would be growing still better.

　　7. 某些主語從句中的謂語動(dòng)詞要用虛擬語氣

　　某些表示命令，要求，決定，建議，主張以及“重要性”和“緊迫性”等概念的主語從句中謂語動(dòng)詞要用虛擬語氣。這時(shí)，謂語動(dòng)詞用動(dòng)詞原形或should +動(dòng)詞原形。這類主語從句一般由 “It is (was) + 形容詞/過去分詞 + that引導(dǎo)的從句”構(gòu)成。該結(jié)構(gòu)中，常用的形容詞主要有：advisable, appropriate, desirable, essential, imperative, important, necessary, obligatory, proper, urgent, vital等;常用的過去分詞主要有：arranged, decided, demanded, desired, ordered, proposed, recommended, requested, suggested等。

　　It is necessary that you (should) stop smoking so heavily.

　　It is arranged that you (should) enter for this competition.

　　8. as if / though引起的從句

　　當(dāng)as if / though引起的從句所表達(dá)的內(nèi)容完全與實(shí)際情況相反或者純粹是一種假設(shè)時(shí)，通常要用虛擬語氣。如果從句表示與現(xiàn)在的事實(shí)相反，謂語動(dòng)詞用一般過去時(shí);如果從句表示與過去的事實(shí)相反，謂語動(dòng)詞用過去完成時(shí);如果從句表示與將來的事實(shí)相反，謂語動(dòng)詞用would (might, could) + 動(dòng)詞原形;

　　They talked as if they had been friends for years.

　　I remember the whole thing as if it happened yesterday.

　　It looks as if it might rain.

　　Note: 如果as if / though引起的從句所表達(dá)的內(nèi)容被看作是事實(shí)或者有可能是真實(shí)的，則要用陳述語氣。

　　It seems as if it is going to rain.

　　The meat tastes as if it has already gone bad.

　　9. lest, for fear that和 in case引起的從句

　　當(dāng)lest, for fear that和 in case表示“以免，以防，生怕，惟恐”等時(shí)，在它們引起的從句中，謂語動(dòng)詞常用should + 動(dòng)詞原形。

　　He ran away lest he should be seen.

　　He’s working hard for fear that he should fall behind.

　　He left early in case he should miss the last train.

　　10. If only引出的從句

　　If only引出的從句用以表達(dá)感嘆性的愿望，常譯為“要是…就好了”。If only從句經(jīng)常省略結(jié)果主句，且主要用在虛擬語氣中，即從句的謂語動(dòng)詞用一般過去時(shí)表示現(xiàn)在或?qū)�來不可能�?shí)現(xiàn)的愿望，或用過去完成時(shí)表示過去沒有實(shí)現(xiàn)的愿望。

　　If only the rain would stop.

　　If only I’d listened to my parents.

　　Note: if only引出的句子偶爾也可使用陳述語氣，但考生須注意的是，在各類測試中一般都以用虛擬語氣為正確答案。

　　11. would rather(that)引出的從句

　　would rather意為“寧愿”，接從句時(shí)常省略關(guān)系代詞that。would rather后的從句要用虛擬語氣，即從句謂語動(dòng)詞用一般過去時(shí)表示現(xiàn)在或?qū)�來的愿望，用過去完成時(shí)表示與過去事實(shí)相反的愿望。

　　I’d rather you told me the truth.

　　I would rather you came tomorrow than today.

　　I’d rather you hadn’t told me about it.

　　12. It is (about/high) time (that) 句型

　　該句型表示“(早)該做…”，其后的定語從句中的謂語動(dòng)詞要用虛擬語氣表示。在測試中從句的謂語動(dòng)詞用一般過去時(shí)。

　　It is time that we went to bed.

　　It is high time that somebody taught you to behave yourself.