353. 混合时间条件句的用法：
i. 有时条件从句的动作和主句动作发生的
时间不一致。这时动词的形式，应根据它所要表达的具体时间来决定用什么形式。
b) If she hadn’t trained so hard, she wouldn’t be run so fast.(从句叙述过去，主句叙述现在。)
i. (fact: she has trained very hard, so she would able to run fast.)
ii. You would speak English well enough if
you had practised reading and speaking it every day.(主句叙述现在，从句叙述过去)
iii. (fact: You didn’t practice (hasn’t practiced ) reading and speaking it every day, so you can’t speak English well enough.)
iv. 在其他状语从句中的用法
c) 主要用于由as if (as though) 引导的比较状语从句，从句中谓语动词一般用“动词的过去式(be 变were )或had +过去分词。”
i. 如：
ii. She looked as if she were ill.(实际上她没有病，在这里用虚拟语气补语比喻她精神不佳)
iii. Xiao Liu speaks English so well as if
he had studied in England.(这里用虚拟语气表现他的 英语说得好)
iv. (2)、在主语从句中的用法：
v. 通常由形式主语it引出的主语从句来表达。主语从句中，谓语动词用“should+动词原形”；表示“必要”“重要”“奇怪”等意思。
vi. It is necessary that you should clean
the workshop after work.下班后你必须清扫车间。
vii. It is important that we should ask
advice of other people about our work.在工作中，征求别人的意见是很重要的。
在宾语从句中的用法(详见《高一上学期英语语法重难点集汇》)
