THE MEN WERE VERY STRONG AND HEALTHY. ALTHOUGH THEY ... FOR MORE T...

21. - 70 DE THI CHUNG CHI B TIENG ANH
70 DE THI CHUNG CHI B TIENG ANH

21. The men were very strong and healthy. Although they ... for more than three hours, they

did not need a rest.

a. were walking

b. have walked

c. have been walking

d. had been walking

d