The habit is something that someone does repeatedly and often does not because they have

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A. know
B. understand
C. experience
(答案→)D. realize
解析：答案：D　考查动词辨析。句意为：习惯是人们不断重复却通常没有意识到的行为，因为他们曾经做过多次了。know意为“知道，懂得”；understand意为“理解”；experience意为“经历，体验”；realize意为“意识到”。根据句意可知，D项正确。