備戰2020屆高考英語（通用版）一輪復習專題04 名詞性從句
（1）在引導賓語從句時whether與if可互換，但如果和or not連用則只用whether。如：
i don’t know whether or not he can stay here longer.
（2）如果賓語從句是否定結構，則用if而不用whether引導。如：
he asked me if i wasn’t going there.
（3）介詞賓語從句只能用whether引導。如：
i’m not interested in whether he is rich.
（4）引導主語從句、表語從句或同位語從句一般多用whether。如：
the question is whether you can do it yourself.
the question whether he will come here himself isn’t decided yet.
whether it will do us harm or good remains to be seen.
（5）用it作形式主語時，whether或if都可以引導主語從句。如：
it is not clear to me whether/if he likes the present.
4.注意what/whatever；who/whoever；which/whichever的區別。試比較下列句子：
whoever will go to the concert please signs your name here.=anyone who will go to the concert please signs your name here.
who will go to the concert isn’t known.=it’s unknown who will go to the concert.
he won’t believe whatever she says.=no matter what she says，he won’t believe her.
whichhever toy you want is yours.=no matter which toy you want，it is yours.
5.注意how long/how soon/how often/how much的區別。
how long will he stay here?
他將在這里待多久？
how soon can you be ready?
你多久能準備好？
how often do you visit her?
你多長時間去探望她一次？
how much is that dress?
那件衣服多少錢？
6.當主句謂語動詞表示不肯定或懷疑時，賓語從句用whether/if引導；表示有把握時用that引導。如：
i doubt whether/if he can win the match.
i don’t doubt that he can win the match.
7.what與that在引導主語從句時的區別
what引導主語從句時在從句中充當句子成分，如主語、賓語、表語，而that則不然。如：
what you said yesterday is right.
that she is still alive is a fact.
8.主語從句不可位于句首的五種情況
（1）if引導的主語從句不可居于復合句句首。
（2）it is said/reported...結構中的主語從句不可提前。如：
it is said that president jiang will visit our school next week.（right）
that president jiang will visit our school next week is said.（wrong）
（3）it happens...，it occurs...結構中的主語從句不可提前。如：
it occurred to him that he failed in the examination.（right）
that he failed in the examination occurred to him.（wrong）
（4）it doesn’t matter how/whether....結構中的主語從句不可提前。如：
it doesn’t matter whether he is wrong or not.（right）
whether he is wrong or not doesn’t matter.（wrong）
（5）含主語從句的復合句是疑問句時，主語從句不可提前。如：
is it likely that it will rain in the evening?（right）
is that will rain in the evening likely?（wrong）