Not for a moment that this disease was caused by certain virus.
A. he have doubted
B. he doubts
C. did he doubt
D. he did doubt
网友回答
A. he have doubted
B. he doubts
(答案→)C. did he doubt
D. he did doubt
解析：考查倒装句。当否定词或者半否定词放在句首的时候，后面的主句使用部分倒装的形式。本题中否定词not放在了句首，故使用C正确。