根据句意，写出括号内所给单词的适当形式。
The more books you read, the richer ____________ (know) you will get.
Next week it will be his grandfather’s ____________ (ninety) birthday.
The UK is a ____________ (Europe) country. Like China, it also has a long history.
Cutting down too many trees makes it ____________ (possible) for people to protect wild animals
in the world.