a lot of、lots of、a number of( /large numbers of)、a great deal of、plenty of的区别:五个“名词+介词”短语都表示“大量,许多”,a lot of(或lots of)既可以修饰不可数名词也可以修饰可数名词的复数形式,可以相应地换为much和many;
plenty of“足够、大量”,既可以修饰不可数名词也可以修饰可数名词的复数形式。
a number of / large numbers of只可以修饰可数名词复数形式(它修饰的词作主语时谓语用复数形式)可以换为some、many、a lot of、plenty of。
a great deal of只可以修饰不可数名词(它修饰的词作主语时谓语用单数形式)可以换为much。
如:A lot of people think that time is money.(许多的人认为时间就是金钱。) /
I don’t have to do it in a hurry because I have plenty of time.(我用不着赶忙,因为我有充足的时间。) /
I have a number of letters to write today.(今天我有好多信要写) /
I spend a great deal of time/money on shopping.(在购物方面我花费了大量的时间/金钱。)

再介绍一个小知识:one与ones用来代替上文的一个或多个人或事物,前面可以加冠词、形容词、指示代词which等。如:
Which jacket would you like, this one or that one?(你要哪件夹克,这件还是那件?
I don’t like the green ones.(我不喜欢绿色的那些)