用所给词的适当形式填空。

1. A tractor goes______(fast) than a bike.

2. They don’t use animals to do farm work any ______(many).

3. Which do you like ______(good),this one or that one?

4. The girl is ______(beautiful) in the class.

根据微观经济学的观点，以下哪一种市场的进入难度最大：（）

A、完全垄断

B、寡头垄断

C、垄断竞争

D、完全竞争