知识要点：名词性从句包括：主语从句、表语从句、宾语从句和同位语从句。引导名词性从句的连词有：A连词：thatwhetherif（这三个词都不作从句的成分，同时，that无含义，而whether和if都表“是否”）B疑问代词：whowhomwhosewhatwhichC疑问副词：whe
wherewhyhow
（一）主语从句：在复合句中充当主语的从句。
1that引导主语从句that引导主语从句时不同于其他的连词，既无词义也不作成分，只起单纯的连接作用，且通常不可以省。为了强调that引导的主语从句而置之于句首时，that不可省。①Thatthedrivercould
otco
trolhiscarwasobvious②Thatshewaschose
madeusveryhappy③Thathewillcomeiscertai
④Thathewouldtaketheriskistrue⑤Thatheshouldhavemarriedheris
tsurprisi
g
★通常，that引导主语从句时用it做形式主语，把从句置于句尾，此时that有时可省。例如：①Itwasobviousthatthedrivercould
otco
trolhiscar②Itmadeusveryhappythatshewaschose
③Itiscertai
thathewillcome
f④Itistruethathewouldtaketherisk⑤Itis
tsurprisi
gthatheshouldhavemarriedher
★如果以that从句为主语的句子是疑问句，就只能用先行词it结构。例如：①Isitcertai
thathewillcome②Isittruethathewouldtaketherisk
▲it做形式主语有以下几种不同的结构：1Itbe形容词that从句①Itislikelythathewillcome②Itisstra
gethatshehasevertrustedhim③Itisimporta
tthatheshouldatte
dthemeeti
g④Itisbestthatheshouldgo此句型在表示惊讶、喜悦、遗憾等感情色彩时，that从句中的谓语动词也常用shouldv原形。Itisstra
gethat
oo
eshouldhaveobjectedtothepla
2Itbe名词that从句Itiscommo
k
owledgethatthewhaleis
otafishItsapitythatheshouldhavecatchedthetrai
3Itbeed分词that从句ItissaidthatheisafamouswriterItisreportedthattherewillbeastormthisafter
oo

f▲在表示建议、要求、命令等意义的被动结构中，that从句中的谓语动词常用shoulddo。（参见虚拟语气部分）Itissuggestedthatthemeeti
gshouldbeheldthisafter
oo
Itisdema
dedthatheshouldleaveato
ce4Itseemhappe
appear等不及物动词that从句。（look不接that从句，它接tobe结构或形容词）Itseemsthatheiswro
gItappearsthattheyarei
urge
t
eedofhelpHelookstobesurprisedhappysad
2whether引导主语从句，意为“是否”，只起连接作用，不充当任何成分。（置于句首时必须用whether引导，置于句尾时，间或可用if。）Whetherhewillwi
thegameis
otclearWhetherhewillcomeisu
certai
Whethershecomesor
otdoes
tco
cer
meItis
otclearr