5. It's polite to finish eating everything on your plate, so don't take more food than you need. 餐盤里的東西要吃光才禮貌，所以不要多拿。

該句中的it為形式主語，真正的主語為to finish eating …例如：It's not right to tell lies. 撒謊是不對的。

it作為形式主語，真正的主語是動詞不定式短語。常見的句型有：

4. Having good table manners means knowing, for example, how to use knives and forks, when to drink a toast and how to behave at the table. 在餐桌上，懂禮節(jié)意味著你知道如何使用刀叉，何時祝酒以及如何在用餐時舉止得體。

該句中having good manners為v-ing形式作主語。例如：Collecting stamps is one of his hobbies.

▲友情提示：在v -ing 形式前加形容詞性物主代詞或名詞所有格，構(gòu)成v -ing復(fù)合結(jié)構(gòu)，在句中作主語、賓語。

[考例5](2001上海)Fishing is his favorite hobby, and ____.

　　 A. he'd like to collect coins as well

　　 B. he feels like collecting coins, too

　　 C. to collect coins is also his hobby

　　 D. collecting coins gives him great pleasure

[考查目標(biāo)]v -ing 作主語。

[答案與解析]D　 A、B、C三項句法都無錯誤，但在and連接的并列句中，兩個簡單句的主語要保持一致的形式 fishing and collecting coins分別做兩個簡單句的主語。

3. When asked about the secret of his success, Steven Spielberg said that he owes much of his success and happiness to his wife and children. 當(dāng)有人問起他成功的秘訣時。史蒂文·斯皮爾伯格說起他的成功和幸福主要來自于妻子和孩子。

該句中的 "when" 是時間狀語從句的省略形式。在狀語從句中，如果從句主語與主句主語一致或從句主語是it，而且從句謂語動詞是be或包含be時，常常將從句主語與be省略。例如：Although born in Chicago, the author is famous for his stories about New York.

[考例] (2003上海春招) Unless ___to speak，you should remain silent at the conference.

　　 A. invited　　　　 B. inviting

　　 C. being invited　　 D. having invited

[考查目標(biāo)]狀語從句的省略現(xiàn)象。

[答案與解析]A unless為連詞，后面省略了you are，所以選invited。

2. Many people who saw the film were afraid to swim in the sea when they remembered the scenes in which people were eaten by the shark. 好多看過這個片子的人一想起片中鯊魚食人的場面．就不敢下海游泳了。

該句是一個復(fù)雜長句，從when到句子末尾是狀語從句，在從句中包含一個由which引導(dǎo)的定語從句，修飾先行詞scenes; 在前面的主句里面。包含一個由who引導(dǎo)的定語從句，修飾先行詞people。例如：Those who want to go camping next Sunday sign your name here before class is over.

定語從句關(guān)系詞的選擇，要遵循“瞻前顧后”的原則，所謂“瞻前”即看前面的先行詞指人還是指物；“顧后”即后面的定語從句，看關(guān)系詞在定語從句中作什么成分。例如：This is the factory where he works. (狀語) / This is the factory (that / which) he visited. (賓語)

[考例](NMET 1992)In the dark street，there wasn't a single person ____ she could turn for help.

　　 A. that　　 B. who　 C. from whom　　 D. to whom

[考查目標(biāo)]定語從句。

[答案與解析]D “turn to sb for help”為固定短語，意思是“向某人求助”，所以選to whom。

2. why在句中是關(guān)系副詞，引導(dǎo)定語從句，修飾先行詞reason，同時它在定語從句中作狀語，此時why = for which，但要注意：關(guān)系詞在定語從句中作主語或賓語時，要用關(guān)系代詞that或which。

[考例](2002上海春招)Is this the reason ____ at the meeting for his carelessness in his work?

　　 A. he explained　　　　 B. what he explained

　　 C. how he explained　　 D. why he explained

[考查目標(biāo)]定語從句。

[答案與解析]A　 what，how不能引導(dǎo)定語從句，排除B、C兩項；the reason在定語從句中作explained的賓語，可填that / which，或者也可以省略。

1. 句中that引導(dǎo)的表語從句說明主語reason的具體內(nèi)容，往往被看作是固定句型：The reason is / was that clause. 當(dāng)主語是reason / cause時，一般不能用because或why引導(dǎo)表語從句，以免造成語意重復(fù)。當(dāng)主語是This / That時，可以由because / why引導(dǎo)表語從句。例如：One reason is that people traveled to America from all European countries.

[考例](NMET 1999)

-- I drove to Zhuhai for the air show last week.

-- Is that ____ you had a few days off?

　　 A. why　 B. when　 C. what　 D. where

[考查目標(biāo)] 表語從句。

[答案與解析]A　 句子的意思是“那就是你請了幾天假的原因嗎?”因此可知答案為why。

1. The reason why he could not go there was that his grades were too low. 他沒能上電影學(xué)院是因為他的分?jǐn)?shù)太低了。

該句巾的why引導(dǎo)一個定語從句，而that引導(dǎo)表語從句。

5. If you had gone ____ your test paper carefully before handing it in you would have made fewer mistakes.

☆句型詮釋☆

4. -- What do you think the contest? -- I was told that the English Speech Contest went ____ successfully last night.

3. The market was filled ____ salted fish, giving the worst smell that you can imagine.