As is known to all, theory is based on practice and serves practice.
A. in hand
B. in turn
C. in return
D. in exchange
网友回答
A. in hand
(答案→)B. in turn
C. in return
D. in exchange
解析：考查词组辨析。In hand在手头，在控制中 in turn轮流，反过来（作用于） in return 作为回报 in exchange 交换 本句意为，众所周知，理论建立在实践的基础之上，反过来服务于实践。