a lot of,a large amount of,a large sum of.a number of在用法伤有啥区别呀?具体点滴,

a large number of 表示许多的,只能修饰可数名词；a lot of等于lots of,即可修饰可数的,又可修饰不可数名词；plenty of也是修饰可数或不可数名词,与a lot of同义但不如其常用；a great many只能修饰可数名词,等于a good many.记住这些在使用时就不会混淆了.例句：
1、A large number of high-tec products have(has) been made in that factory(那个工厂生产了许多高科技产品）a number of做主语时,动词可用单数,也可用复数.
2、Don't hurry.We still have plenty of time.
There are plenty of such persons in our school.可数和不可数都可以.
3、He got a lot of(lots of)homework(things)to do after school.可数和不可数都可以.
4、They raised a great many(a good many)proposals at the meeting.只能是可数的.
此外,表示大量,许多的还有a large quantity of,修饰可数和不可数名词,如：
As a result of destroying the forests,a large quantity of desert has coverd the land(毁林导致了大量土地的荒漠化）.On that day she received a large quantity of flowers.