It is believed that if a book is it will surely the reader.A. interested; interestB. in

问题补充：

It is believed that if a book is , it will surely the reader.

A. interested; interest

B. interesting; be interested

C. interested; be interesting

D. interesting; interest

答案：

A. interested; interest

B. interesting; be interested

C. interested; be interesting

(答案→)D. interesting; interest

解析：前者是作表语，表示“(令人)有趣的”，用interesting，后者是在will后作谓语，用动词原形，表示“使(人)有趣”是interest。