The book by him is difficult .A. wrote; understandingB. written; to be understoodC. writi

问题补充：

The book by him is difficult .

A. wrote; understanding

B. written; to be understood

C. writing; understand

D. written; to understand

答案：

A. wrote; understanding

B. written; to be understood

C. writing; understand

(答案→)D. written; to understand

解析：考查非谓语动词，第一空是过去分词作定语用written，difficult后用不定式主动表被动。句意：被他写的这本书很难理解。所以选D。