a number of後只能接可數名詞,如果在a後面再加great就變a great number of就等於many(many修飾可數名詞）另外還有一個the number of,它們的區別就是,the number of後面加單數動詞,舉個例句,The number of students in our class is fifty(注意這個is是單數動詞）,a number of後面加複數動詞,舉個例句,A number of students in our class are from Shanghai(注意這個are是複數動詞）,a lot of 既可接可數又可接不可數名詞,另外a lot of 就等於lots of。

a number of意思是“許多”，相當於 many，修飾可數名詞複數。作主語時，謂語動詞用複數。

如：

She retained a number of copies for further annotation.

她保留了許多副本以便作進一步的註解。

This view is contrary to the aims of critical social research for a number of reasons之所以說此觀點違背了批判性社會研究的宗旨，有幾點理由。

A number of houses were burnt down in the fire.在火災中，好些房子給燒燬了

a lot of
a lot of與lots of的意思和用法完全相同，都是起形容詞作用的片語，可用於修飾可數或不可數名詞。相當於many或much. 

如： 
There are a lot of / lots of famous movie stars in the USA. 美國有許多著名的電影明星。

We need a lot of [lots of] money. 我們需要很多錢。

He has quite a lot of [lots of] friends. 他有很多朋友。

A lot of people think that time is money.(許多的人認為時間就是金錢。)

修飾主語時，謂語的數取決於它所修飾名詞的數。

如：

A lot of money was spent on it. 在它上面花了很多錢。

A lot of people were interested in it. 對此感興趣的人很多。