Câu hỏi: Certain courses are compulsory; others are optional.

A. voluntary

B. free

C. pressure

D. mandatory

Câu 1: I've put the cake on a high shelf where he can't get at it.

A. low

B. untouchable

C. far

D. difficult to reach

Câu 2: Population growth rates vary among regions and even among countries within the same region.

A. fluctuate

B. stay unchanged

C. restrain

D. remain unstable

Câu 3: It must be difficult to cope with three small children and a job.

A. easy

B. free

C. confusing

D. tricky

Câu 4: You can find the answer to almost any question in cyberspace.

A. require

B. comment

C. answer

D. sentence

Câu 5: You did a beautiful thing in helping those poor children.

A. meaningful

B. good

C. terrible

D. positive

Câu 6: The earth is being threatened and the future looks bad.

A. done

B. made

C. protected

D. varied