根据句意，用括号内所给词的适当形式填空。
After so many ________ (year) practice, Li Na is a well-known tennis player.
We’ll have a surprise party for my mother’s ________ (forty) birthday next Saturday.
The higher the mountain is, the ________ (thin) the air is.
To tell the ________ (true), I don’t like the drinks in that café.
It’s a (an) ________ (usual) experience, few people have chances to do it.