2018高考二輪復習英語教案: 介詞和連詞
9、whether, if引導從句的用法區別：
①引導主語從句、表語從句或同位語從句時，用whether，不用if。例如：whether they will go to the great wall is not known./ the question is whether we can finish the task on time./ the question whether we will take part in the physics contest has not been decided.
②whether可接不定式，而if則不可。例如：i haven’t decided whether to leave or not.
③whether可作介詞的賓語或置于句首表示強調，而if則不可。例如：everything depends on whether we have enough money./ whether he will come, i am not sure.
④whether和if均可引導賓語從句， whether引導的賓語從句一般都是肯定句，if引導的賓語從句可以是肯定的，也可以是否定的（此時不能用whether），例如：could you tell us whether/ if it rains in winter in australia?/ i wonder if it doesn’t rain.
⑤引導賓語從句的whether和if常可與or not連用。連用時要注意or not的位置，它一般與 whether、if分開使用，有時它可與whether合起來使用，但不能與if合起來使用。例如：i don’t know whether/ if they will come or not./ i don’t know whether or not they will come.
⑥if可用來引導條件狀語從句，譯“如果”，whether則不行。例如：if you work hard, you are sure to succeed.
10、as作從屬連詞可引導多種狀語從句。①as引導時間狀語從句，意為“當…時”。例如：as (he was) a young man, he was a storekeeper and later a postmaster./ he sang as he worked. ②as引導方式狀語從句，意為“象…一樣”。例如：we must do as the party teaches us. ③as引導原因狀語從句。意為“由于”，例如：as you are tired, you had better rest. ④as引導讓步狀語從句。意為“雖然”、“盡管”child as he is, he can do it well. ( = although he is a child, he can do it well.) 另外，as做為關系代詞還可以引導定語從句，如：i have the same book as you。.