The conference has been held to discuss the effects of tourism the wildlife in the area.A

问题补充：

The conference has been held to discuss the effects of tourism the wildlife in the area.

A. on

B. in

C. at

D. of

答案：

(答案→)A. on

B. in

C. at

D. of

解析：句意：会议已经被举行来讨论在这个地区旅游对野生动物的影响。the effect on sth 对…的影响，习惯搭配，故选A