If you reading that book take it back to the library.A. have finishedB. will finishC. fi

问题补充：

If you reading that book, take it back to the library.

A. have finished

B. will finish

C. finished

D. are finishing

答案：

(答案→)A. have finished

B. will finish

C. finished

D. are finishing

解析：句意：如果你已经读完了那本书，把它放回到图书馆。根据句意可知，如果你已经读完，这里强调的是结果“完成”。故用现在完成时。在条件状语从句中，用现在完成时代替将来完成时。故选A。