Some researchers believe that there is no doubt a cure for AIDS will be found.A. whichB.

问题补充：

Some researchers believe that there is no doubt a cure for AIDS will be found.

A. which

B. that

C. what

D. whether

答案：

A. which

(答案→)B. that

C. what

D. whether

解析：句中a cure for AIDS will be found是对no doubt的完全解释，所以这里需要引导同位语从句的引导词that。