I don’t doubt he took the first place in his class; but I do doubt he will succeed in the end.
A. if; that
B. but; which
C. whether; whether
D. that; whether
网友回答
A. if; that
B. but; which
C. whether; whether
(答案→)D. that; whether
解析：本题考查动词用法。doubt在肯定句中用关系词whether/if，在否定句中用关系词that,故选D。