a variety of 和 varieties of的区别?
在Longman中的答案：
a variety of something：a lot of things of the same type that are different from each other in some way,e.g.
The girls come from a variety of different backgrounds.
variety of:a type of thing,such as a plant or animal,that is different from others in the same group,e.g.
The lake has more than 20 varieties of fish.