B. with

C. on

D. at

31.The atmosphere _______ certain gases mixed together in definite proportions.

( C )

A. composes of

B. is made up

C. consists of

D. makes up of

32.He didn’t have time to read the report word for word. He just

_______ it.

( A )

A. skimmed

B. observed

C. overlooked

D. glanced

33.He _______ at the thought of seeing the pretty girl again.

( B )

A. cheered off

B. cheered up

C. cheerful

D. cheered on

34.Knowing first aid (急救) is _______ to saving lives.

( C )

A. cure