Theory is based on practice and serves practice. A. in turnB. by and by C. by chanceD. in

问题补充：

Theory is based on practice and serves practice.

A. in turn

B. by and by

C. by chance

D. in this case

答案：

(答案→)A. in turn

B. by and by

C. by chance

D. in this case

解析：短语辨析. A.依次;轮流 B. 不久以后C. 意外的 D.既然这样.句意:理论基于实践并反过来为实践服务.结合语境可知选A.