3．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.
二．代词指代一致问题
代词指代一致是指指代的名词在性、数、格上是否一致，或者所照应的名词词组在某些方面保持一致。
Each cigarette a person smokes does some harm, and eventually he may get a serious disease form its effect.
这里he指代前面的person。
It was during the 1920’s that the friendship between the two American writers Hemingway and Fitzgerald reached its highest point.
这里its指代前面的两人的friendship。
Our department was monitored by two supervisors, Bill and me.
这里me必须用宾格形式。
代词指代一致必须注意以下几个原则和规律：
1．邻近和靠近原则
由either … or, neither…nor, not only…but (also)连接先行词时候，如果两个先行词在数和性上保持一致，就用其相应的一直的人称代词；如果两个先行词在数或性上不一致，人称代词一般与邻近的先行词在数和性上保持一致。
Neither Mary nor Alice has her key with her.
Neither the package nor the letters have reached their destination
If either David or Janet comes , he or she will want a drink
2．当no one, everyone, each,everybody, none ,anybody, someone, somebody用作主语或主语的限定词时候,或者anything, nothing, something everything等不定代词作主语时候，其相应的代词一般按照语法一致原则，采取单数形式。如：
Everybody talked at the top of his voice.
None of the boys can do it , can he?
Everything is ready, isn’t it?
3．当主语为复数形式，后跟each作同位语时，如果each位于动词之前，其后的代词或相应的限定词用复数形式；如果 each位于动词之后，其后的代词或相应的限定词用单数形式。如：
They each have two coats
we are each responsible for his own family
4．由and连接两个先行词，代词用复数
如：the tourist and businessmen lost their luggage in the accident
（四） 主谓一致问题
主谓一致是指主语与谓语在数上要一致。把握主谓一致问题，考生主要解决的是对不同结构的主语单复数的认定，进而选择适当的谓语。解决主谓一致主要遵循三个原则：
语法一致原则
意义一致原则
就近一致原则
很多情况下应该综合利用这三个原则来处理主谓一致，在不同情况下可能应用三个原则中的不同原则，具体应用哪种原则应该视具体情况而定。总结如下：
一．谓语动词用单数的情况
1．动名词短语、不定式短语、名词性从句做主语，谓语用单数。如：
Buying clothes is often a time-consuming job because those clothes that a person likes are rarely the cones that fit him or her.
(1987年
考研题)
To understand the situation completely requires more thought than has been given thus far.
2．表示时间、距离、金额、重量、面积、体积、容积等度量的名词短语做主语时，谓语用单数。
Two weeks was too long
Five times five makes twenty five
3．一般用and连接的两个单词或短语做主语时候，谓语用复数，但是下面用and连接的主语表示一个概念，谓语用单数：
law and order 法制 soap and water 肥皂水
a cup and saucer 茶杯碟子 fork and knife 刀叉
the needle and thread 针线 trial and error 反复尝试，不断摸索
horse and carriage 马车 time and tide 岁月
bread and butter 奶油面包 the ebb and flow 盛衰，潮涨潮落
如： If law and order not preserved, neither the citizen nor his property is safe.
A. is B. are C. was d. were
答案：A。
4．表示学科和某些疾病名称的名词是复数形式，作主语时候谓语动词用单数形式
Linguistics is a branch of study on human language.
5．有些名词形式上是复数，意义上是单数，根据意义一致原则动词用单数
The chaos was stopped by the police
The news is a great encouragement to us
A series of debates between the lectures was scheduled for the next weekend.
6．用and 连接的成份表示一个单一概念时候，动词谓语用单数形式
Bread and butter is our daily food
Time and tide waits for no man
二． 谓语用复数情况
1． 由and, both …and, 连接的并列主语，和both ,a few, many ,several 等修饰语后面谓语动词通常用复数形式。
Few people know he and I were classmates when we were at college.
2．集体名词police, public, militia, cattle ,class ,youth后常用复数形式的动词
The Chinese people are brave and hardworking
The cattle are grazing in the sunshine
3．当表示民族的词与冠词合用当主语，谓语动词用复数形式
The Japanese were once very aggressive
4．某些形容词前面加定冠词表示一类人，做主语时候，谓语动词用复数
The rich are not always selfish
5．不可数名词作主语，其前有表示数量的复数名词修饰时，谓语动词用复数
Three million tons of coal were exported that year
