谓语动词常用单数的情况
1）名词性从句及不定式、动名词作主语时，谓语动词一般用单数形式。
【例如】
To finish the work in advance is what he wants.
Smoking cigarettes is dangerous to your health
What seems easy in theory is difficult in practice.
What caused the accident is a complete mystery.
但是，what引导名词从句作主语时，其表语是复数形式时，系动词也可以是复数形式。
【例如】
What we badly need here are qualified teachers.
2）当主语是单数，后面跟着由including, with, together with, along with, like, in addition to, as well as, rather than, but, except, more than, accompanied by等连接的短语时，谓语动词用单数。
【例如】
Mary as well as her sister likes listening to music.
Doctor Richards, together with his wife and three children, is to arrive on the afternoon flight.
My best friend rather than anyone else has got the first prize in the speech contest.
3）one, one of, every, everyone, everybody, each, many a, either, neither, no one, nobody, anyone, anybody, someone, somebody用作主语或修饰主语时，谓语动词用单数形式。
【例如】
Each man, woman and child has the same right.
Many a student doesn't like to do their homework.(many a student＝many students）
Either of students is going to compete for the president of the students' union.More than one person was involved in the case.
Neither of the young men who had applied for a position in the university ____.
A） has been accepted
B） have been accepted
C） was accepted
D） were accepted
neither用作主语或修饰主语时，谓语动词用单数形式。此外，定语从句用过去完成时，主句应用一般过去时，故答案为C。
4）and所连接的两个单数名词作主语，指同一人、同一件事或同一概念时，其谓语动词用单数。例如：My best friend and adviser has changed his mind again.
Bread, butter and eggs is typical American Breakfast .
If law andsgroupsis not preserved, neither the citizen nor his property is safe.如果不能维持治安，公民和他的财产都不安全。
5）表示时间、距离、重量、体积、金钱的复数名词，作主语时作为整体来看待，谓语动词通常用单数。
【例如】
Five thousands dollars is quite a large sum of money to me.
Fifty miles is too long a distance for one to walk on foot.
Ten years has passed but he didn't change at all.
6）“a portion of , a series of, a kind of, a body of, a species of, a pair of+名词”作主语时，其谓语动词一般用单数形式。
【例如】
A series of accidents has occurred recently in America.
A pair of new glasses is quite expensive.
7）事件、机构、国名、作品等专有名词作主语时，谓语动词用单数。
【例如】The Adventures of Huckleberry Finn was written by Mark Twain and it is an interesting book.The United Nations is an organization to defend world peace.