前面給大家講解了公共英語(yǔ)等級(jí)考試pets3語(yǔ)法必備知識(shí)點(diǎn)名詞性從句，本節(jié)我們繼續(xù)為大家講解pets3相關(guān)的語(yǔ)法：虛擬語(yǔ)氣。供大家學(xué)習(xí)參閱。
    3 混合條件句
    有時(shí)，主句與從句的動(dòng)作發(fā)生在不同的時(shí)間，主句從句謂語(yǔ)動(dòng)詞的虛擬語(yǔ)氣形式因時(shí)間不同而不同，這種條件句叫做混合條件句。例如：
    If you had asked him yesterday, you would know what to do now. 如果你昨天問(wèn)過(guò)他，今天就知道做什么了。
     （從句與過(guò)去事實(shí)相反，主句與現(xiàn)在事實(shí)相反。）
    If it had rained last night（過(guò)去）, it would be very cold today （現(xiàn)在）.如果昨晚下過(guò)雨，今天就會(huì)很冷了。
    4 虛擬條件句的倒裝
    虛擬條件句的從句部分含有were, should, 或had時(shí), 可省略if，再把were, should或had 移到從句的句首，實(shí)行倒裝。例如：
     Were they here now, they could help us. =If they were here now, they could help us.他們現(xiàn)在在的話，就會(huì)幫助我們了。
     Had you come earlier, you would have met him. =If you had come earlier, you would have met him.你來(lái)得早一點(diǎn)，就碰到他了。
     Should it rain, the crops would be saved. =Were it to rain, the crops would be saved.假如下雨，莊稼就有救了。
    注意：在虛擬語(yǔ)氣的從句中，動(dòng)詞'be'的過(guò)去時(shí)態(tài)一律用"were"，不用was，即在從句中be用were代替。例如：
     If I were you, I would go to look for him. 如果我是你，就會(huì)去找他。
     If he were here, everything would be all right. 如果他在這兒，一切都會(huì)好的。
    典型例題
     _____ to do the work, I should do it some other day.
    A. If were I　　 B. I were　C. Were I　D. Was I
    答案C. 在虛擬條件狀語(yǔ)中如果有were, should, had這三個(gè)詞，通常將if省略，主語(yǔ)提前, 變成 were, should, had +主語(yǔ)的形式。但要注意，在虛擬條件狀語(yǔ)從句中，省略連詞的倒裝形式的句首不能用動(dòng)詞的縮略形式。如我們可說(shuō) Were I not to do, 而不能說(shuō) Weren't I to do。