They for sixteen hours and still have a long way to go.A. had walkedB. have been walkingC

问题补充：

They for sixteen hours and still have a long way to go.

A. had walked

B. have been walking

C. walked

D. had been walking

答案：

A. had walked

(答案→)B. have been walking

C. walked

D. had been walking

解析：可联系答.案.网客服索取。