謂語動詞常用單數的情況
1）名詞性從句及不定式、動名詞作主語時，謂語動詞一般用單數形式。
【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引導名詞從句作主語時，其表語是復數形式時，系動詞也可以是復數形式。
【例如】
What we badly need here are qualified teachers.
2）當主語是單數，后面跟著由including, with, together with, along with, like, in addition to, as well as, rather than, but, except, more than, accompanied by等連接的短語時，謂語動詞用單數。
【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用作主語或修飾主語時，謂語動詞用單數形式。
【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用作主語或修飾主語時，謂語動詞用單數形式。此外，定語從句用過去完成時，主句應用一般過去時，故答案為C。
4）and所連接的兩個單數名詞作主語，指同一人、同一件事或同一概念時，其謂語動詞用單數。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.如果不能維持治安，公民和他的財產都不安全。
5）表示時間、距離、重量、體積、金錢的復數名詞，作主語時作為整體來看待，謂語動詞通常用單數。
【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+名詞”作主語時，其謂語動詞一般用單數形式。
【例如】
A series of accidents has occurred recently in America.
A pair of new glasses is quite expensive.
7）事件、機構、國名、作品等專有名詞作主語時，謂語動詞用單數。
【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.