The tourists are all interested the Great Wall.A. on visitingB. to visitC. in visitingD. v

问题补充：

The tourists are all interested the Great Wall.

A. on visiting

B. to visit

C. in visiting

D. visiting

答案：

A. on visiting

B. to visit

(答案→)C. in visiting

D. visiting

解析：be interested in 表“对……感兴趣”是固定短语，只有C符合题意。本句的意思是“游客们都对参观长城感兴趣。”所以本题选C。