2.谓语动词用单数形式的情形：

⑴不定式短语、动名词及名词从句作主语时，谓语动词用单数形式。如：
To become doctors is their ambition.
Reading without comprehension is no good.
What that country needs is more jobs and lower taxes.

⑵表示时 间、距离、重量、长度、价值等的名词，不论单复数，当作主语时，谓语动词均用单数形式。如：
Twenty years is a long period of his life.
Five thousand dollars is more than I can afford.

⑶用and连接的名词或代词前有every， each， no， many a等修饰时，谓语动词用单数。如：
Every one of the figures was checked at least twice.

⑷事件、国名、机构名称、书籍及其它作品的名称作主语时，谓语动词均用单数形式。
The United Nations was formed in 1945.
Great Expectation is a very famous novel.

⑸限定词（each， every， one， many a， not only one， either， neither等）作主语或修饰主语时，谓语动词一般是单数。如： Each of the students has a studying plan.
Every cook praises his own broth.

⑹and连接的两个名词或代词作主语时，如果指的是同一个人或指一种整体事物时，根据概念一致的原则，后面的动词要用单数形式。特别是and前的名词或代词前有冠词the，而and后的名词或代词前没有冠词the，须用单数谓语。
Ham and eggs is often preferred to hamburgers.
The manager and secretary was present at the meeting.
这类名词还有：fish and chips， bread and butter，law and order，a cup and saucer，the needle and thread等。

⑺短语“a deal （amount， proportion， quantity） 不可数名词”、“a portion （kind， series， species） of 名词“作主语时，谓语动词用单数。
A large amount of oil was spilt on the road.
A portion of goods has been transported to the city.

⑻“the number of …”作主语时，谓语动词也用单数形式。如：
The number of students is increasing every year in the school.

3.谓语动词用复数形式的情形：

当主语是下列情况时，谓语动词只能用复数形式。

⑴由and或both…and…连接的短语作主语。（2.中的⑹例外）
Both he and I are good at English.

⑵常以复数形式出现的名词作主语。如：clothes， pants， shears， riches， remains等。

⑶quantities后面的名词无论是可数名词的复数还是不可数名词，谓语都用复数形式。如：
Large quantities of steam are used by modern industry in the generation of power.

⑷“a number （group等） of…”作主语。如：
A number of people are in the meeting room now.

⑸不可数名词前有表示数量的复数名词修饰。如：
Six hundred square meters of housing have been built.

⑹只能看作复数的集合名词作主语。这类集合名词有：cattle， poultry， youth， clergy， police，people， militia， vermin等。
The cattle were grazing at the foot of the hill.

⑺当两个形容词用and连接来修饰一个单数名词，实指两个事物时，谓语动词用复数形式。如：
The third and the fourth page are missing.