高考英語復習高一下學期語法重難點集匯
if it should rain tomorrow, our picnic would be put off.(that would be out of our expectation.)
if it were to rain tomorrow, our picnic would be put off. (條件從句謂語動詞用were to +動詞原形，表示 下雨的可能性極小。were to rain和should rain 都表示“出乎意料之外”，但were to加強表示“當初沒想到以后的事”)
c. 混合時間條件句的用法：
有時條件從句的動作和主句動作發生的 時間不一致。這時動詞的形式，應根據它所要表達的具體時間來決定用什么形式。
1） if she hadn’t trained so hard, she wouldn’t be run so fast.（從句敘述過去，主句敘述現在。）
（fact: she has trained very hard, so she would able to run fast.）
2)you would speak english well enough if you had practised reading and speaking it every day.(主句敘述現在，從句敘述過去)
（fact: you didn’t practice (hasn’t practiced ) reading and speaking it every day, so you can’t speak english well enough.）
2、 在其他狀語從句中的用法
主要用于由as if (as though) 引導的比較狀語從句，從句中謂語動詞一般用“動詞的過去式（be 變were ）或had +過去分詞。”
如：
she looked as if she were ill.(實際上她沒有病，在這里用虛擬語氣補語比喻她精神不佳)
xiao liu speaks english so well as if he had studied in england.(這里用虛擬語氣表現他的 英語說得好)
（2）、在主語從句中的用法：
通常由形式主語it引出的主語從句來表達。主語從句中，謂語動詞用“should+動詞原形”；表示“必要”“重要”“奇怪”等意思。
it is necessary that you should clean the workshop after work.下班后你必須清掃車間。
it is important that we should ask advice of other people about our work.在工作中，征求別人的意見是很重要的。
（3） 在賓語從句中的用法（詳見《高一上學期英語語法重難點集匯》）