Câu hỏi: It is difficult to write rules that tell exactly when we should apologize, and it is not difficult to learn how to do it.

A. difficult

B. that

C. when

D. and

Câu 1: The office manager insists that his staff use all of their vacation time, but he hardly never takes a vacation himself.

A. insists

B. use

C. their

D. hardly never

Câu 2: Ours brains are incredibly agile machines, and it's hard to think of anything they do more efficient than recognize face.

A. are

B. anything

C. efficient

D. recognize

Câu 3: By the turn of the century, most of the inventions that were to bring in all the comforts of modern living has already been thought of.

A. By the turn of

B. that

C. were to

D. has already been

Câu 4: A beaver uses its strong front_teeth to cut down trees and peel_off its bark.

A. its

B. front teeth

C. eel off

D. its

Câu 5: Species like snakes, lizards, coyotes, squirrels, and jack rabbits seems to exist quite happily in the desert.

A. like

B. seems to

C. quite happily

D. the

Câu 6: The big problem was that we really did not understand what was happened

A. problem

B. that

C. did not

D. was happened