I think Book 6 is than Book 5.A. much difficultB. very difficult C. more difficultD. the

问题补充：

I think Book 6 is than Book 5.

A. much difficult

B. very difficult

C. more difficult

D. the most difficult

答案：

A. much difficult

B. very difficult

(答案→)C. more difficult

D. the most difficult

解析：句意：我想Book 6比Book 5更难。than比，应用比较级，difficult的比较级是more difficult。根据题意，故选C。