如：Each cigarette a person smokes does some harm, and eventually he may get a serious disease from its effect.
It was during the 1920’s that the friendship between the two American writers Hemingway and Fitzgerald reached its highest point.
Our department was monitored by two supervisors, Bill and me.
2.that的指代作用
that指代不可数名词和单数可数名词(如是复数，用those)，后面通常跟有修饰语，如出现在比较结构中的that of。如：
Conversation calls for a willingness to alternate the role of speaker with that of listener, and it calls for occasional “digestive pauses” by both.
No bread eaten by man is so sweet as that earned by his own labor.
3.one的指代作用
one指代带不定冠词的单数可数名词www.med126.com，复数为ones。the one 指代带定冠词的单数可数名词。如：
A good writer is one who can express the commonplace in an uncommon way.
4.do的替代作用
do代替动词，注意数和时态的变化。如：
For him to be re’elected, what is essential is not that his policy works, but that the public believe that it does.
