Ben was busy taking a training class. we had to wait for himfor half an hour..A. soB. ifC

问题补充：

Ben was busy taking a training class. we had to wait for himfor half an hour..

A. so

B. if

C. or

D. but

答案：

(答案→)A. so

B. if

C. or

D. but

解析：本题难度适中，前后句子是因果关系，答案选A。