问题补充：
It is believed that if a book is, it will surelythe 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：动名词作表语时, 表示主语的内容；现在分词作表语，表示主语的特征或性质。
