連接詞

　　1)當(dāng)由陳述句充當(dāng)賓語(yǔ)從句時(shí)，用that引導(dǎo)，that無(wú)詞義，在口語(yǔ)或非正式文體中常省略。如：

　　He said that he could finish his work before supper.他說(shuō)他會(huì)在晚飯前完成工作。

　　2)當(dāng)由一般疑問(wèn)句充當(dāng)賓語(yǔ)從句時(shí)，用if或whether引導(dǎo)，意為“是否”。如：

　　I don't know if /whether he still lives here after so many years.

　　但在下列情況下只能用whether：

　　在不定式前用whether。如：

　　He hasn't decided whether to visit the old man.他尚未決定是否拜訪那位老人。

　　I don't know whether to go.我不知去否。

　　He hasn't decided whether to go by bus or by train.他還未決定是乘公共汽車(chē)去還是坐火車(chē)去。

　　whether置于句首時(shí)，不能換用if。如：

　　Whether this is true or not，I can't say.這是否真的我說(shuō)不上來(lái)。

　　引導(dǎo)主語(yǔ)從句和表語(yǔ)從句時(shí)宜用whether。如：

　　Whether she will come or not is still a question.她是否能來(lái)還是個(gè)問(wèn)題。

　　The question is whether we can catch the bus.問(wèn)題是我們能否趕上公共汽車(chē)。

　　在具有選擇意義，又有or或or not時(shí)，尤其是直接與or not連用時(shí)，往往用whether(if…or not也可以使用)。如：

　　Let me know whether /if he will come or not.(=Let me know whethe or not he will come)

　　I don't know whether/if he does any washing or not.(=I don't know whether or not he does any washing.)

　　I wonder whether we stay or whether we go.

　　在介詞之后用whether。如：

　　I'm interested in whether he likes English.我關(guān)心的是他是否喜歡英語(yǔ)。

　　We're thinking about whether we can finish the work on time.

　　I worry about whether I hurt her feelings.我擔(dān)心是否傷了她的感情。

　　若用if會(huì)引起歧義時(shí)，則用whether。如：

　　Please let me know if you like the book.可理解為：a. Please let me know whether you like the book.請(qǐng)告訴我你是否喜歡這本書(shū)。B. If you like the book, please let me know.你如果喜歡這本書(shū)，請(qǐng)告訴我。

　　3)如果賓語(yǔ)從句原來(lái)是特殊疑問(wèn)句，只需用原來(lái)的特殊疑問(wèn)詞引導(dǎo)。如：

　　Could you tell me why you were late for the meeting this morning?