His ability has never been in doubt----the question is or not he is prepared to work hard

问题补充：

His ability has never been in doubt----the question is or not he is prepared to work hard.

A. that

B. if

C. where

D. whether

答案：

A. that

B. if

C. where

(答案→)D. whether

解析：whether与or not可以连用，if与or not不可以连用，其他的选项都不与or not连用。故选D。