As is known to all theory is based on practice and serves practice.A. in handB. in turnC

问题补充：

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

答案：

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。