as if和as though引導(dǎo)的從句所敘述的情況與事實(shí)相反時(shí)，從句的謂語動(dòng)詞多用虛擬語氣。在虛擬語氣結(jié)構(gòu)中，用________時(shí)態(tài)來表示現(xiàn)在的情形；用________時(shí)來表示過去的動(dòng)作或狀態(tài)；用________時(shí)表示正在進(jìn)行的動(dòng)作；用________時(shí)表示將要發(fā)生的動(dòng)作。

當(dāng)as if和as though從句的主語和主句主語一致，且從句中含有系動(dòng)詞be的某種形式時(shí)該主語和系動(dòng)詞可以省略。

例如：John paused as if(he was)expecting Mary to speak．

理解下在句子，翻譯句中劃線部分，并歸納其用法：

His exam results were not very good, but we must take into account his long illness．________

理解下在句子，翻譯句中劃線部分，并歸納其用法：

On no account you should attempt this exercise if you're seriously ill．(判斷正誤)________

理解下在句子，翻譯句中劃線部分，并歸納其用法：

Can political friction between the two nations account for the outbreak of the war?________

理解下在句子，翻譯句中劃線部分，并歸納其用法：

Imports from Japan account for 40％ of the total．________