---Do you still smoke heavily?
--- No. In fact, it is two years since I .
A. have stopped smoking B. smoked
D. began to smoke D. started to smoke
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解析：考查since结构。it is two years since I 。ince后面跟延续性动词，表示在动词动作结束后已经两年了。即我不吸烟已经两年了，吸烟这一动作发生在过去，所以用一般过去时态。选B。