Only then did he the effects of his action.A. awareB. aware ofC. become awareD. become awa

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A. aware
B. aware of
C. bee aware
(答案→)D. bee aware of
解析：根据题中only放在句首，主句用倒装结构did he，可知主句用动词词组，故用bee aware of知道，意识到，选D。