as if和as though引导的从句所叙述的情况与事实相反时，从句的谓语动词多用虚拟语气。在虚拟语气结构中，用________时态来表示现在的情形；用________时来表示过去的动作或状态；用________时表示正在进行的动作；用________时表示将要发生的动作。

当as if和as though从句的主语和主句主语一致，且从句中含有系动词be的某种形式时该主语和系动词可以省略。

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

理解下在句子，翻译句中划线部分，并归纳其用法：

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

理解下在句子，翻译句中划线部分，并归纳其用法：

On no account you should attempt this exercise if you're seriously ill．(判断正误)________

理解下在句子，翻译句中划线部分，并归纳其用法：

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

理解下在句子，翻译句中划线部分，并归纳其用法：

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