单选题 When the colonel learned that headquarters had been unable to send him reinforcements, he ______ the order for the scheduled attack.

【正确答案】 A

【答案解析】(countermand撤消命令)。句意为：上校听说司令部未能给他派去援军，他撤消了预定进攻的命令。B．relinquish放弃；C．rephrase给……重新措辞；D．invalidate使无效。