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

A. problem

B. that

C. did not

D. was happened

Câu 1: Mercury and alcohol are widely used in thermometers because their volume increases uniform with temperature.

A. are

B. widely

C. their volume

D. uniform with

Câu 2: 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 3: Mary and her sister just bought two new winters coats at the clearance sale.

A. her sister

B. just bought

C. two new

D. winters

Câu 4: Parks which are found in downtown areas where office workers and store employees can enjoy their lunch hours sitting on the green grass in clean, fresh air.

A. which

B. employees

C. lunch hours sitting

D. fresh air

Câu 5: The eastern bluebird is considered the most attractive bird native of North America by many bird-watchers.

A. bluebird

B. considered

C. native of

D. by

Câu 6: 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