much修饰不可数名词
many修饰可数名词
plenty of 能修饰可数名词和不可数名词
a lot 是副词短语,修饰动词 如 I like it a lot.
a lot of =lots of用来修饰名词 如 I have a lot of books.
例如：1、There is plenty of time.
2、There are plenty of eggs in the basket.