11. Human behavior is mostly a product of learning, ______the  behavior of animal depends mainly on instinct.

A. whereas

B. so

C. unless

D. that

12. Mumps ____ a very common disease which usually affects children.

A. was

B. is

C. are

D.were

13. The _____largest state is, and has been since Alaska’s admission into the Union, Califoria.

A. three

B. third

C. first third

D. most

14. ________ the surface of metal, but also weakens it.

A. Not only does rust corrode

B. Not only rust corrode

C. Rust, which not only corrodes

D. Rust not only corrodes

15. It’s nice to go for a walk __ a summer evening.

A. on

B. in

C. at

D. during

答案：abbda