21.What are national parks’entrance fees mainly used for？

A.Improving public services.

B.Supporting important programs.

C.Resources protection.

D.Fish restoration.

22.Why is a digital pass recommended in the text？

A.One can enter the park easily with it.

B.It can save extra entrance fees.

C.It can be bought conveniently.

D.It can be emailed to the park.

23.How much should you pay if you travel in the park on a bike with a Seven-day Pass？

A.$20.

B.$30.

C.$35.

D.$70.