(1) plenty of, a lot of, lots of均表“许多”，修饰复数可数名词或不可数名词。
　The room contained plenty of (or a lot of or lots of) students.（复数名词）
　The room contained plenty of (or a lot of or lots of) furniture.（不可数名词） 

(2) a great (or a good) deal of, a large (or a small) quantity of, a large (or a small) amount of, 均表（量）， 修饰不可数名词。
　The room contained a great deal of furniture. （不可数名词）
　The room contained a good deal of furniture. （不可数名词）
　The room contained a large quantity of furniture. （不可数名词）
　The room contained a large amount of furniture. （不可数名词）
　The room contained a small quantity of furniture. （不可数名词）
　The room contained a small amount of furniture. （不可数名词） 

　(3) a number of “许多；一些”；a great (large, good) number of “许多”，修饰复数可数名词，并且要与复数动词连用。
　A number of books are missing from the library.
　The number of books from the library is large. 
　The room contained a great (or large or good) number of students.（复数可数名词） 

注：the number of ＋复数名词，意为“……的数量”，后接单数动词。