The policemen regretted as soon as possible at the alarm.
A. not taking action
B. not to take measures
C. taking no actions
D. to take no action
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(答案→)A. not taking action
B. not to take measures
C. taking no actions
D. to take no action
解析：考查非谓语动词。短语：后悔做了某事regret doing sth，否定式应在doing前加not，句意：警察们后悔听到警报后没有尽快采取行动。take action 采取行动，所以选A。