题目：
— Haven't you finished your report yet?
— How I regret ______ the weekend ______ TV! [ ]
A. wasting; to watch
B. to waste; to watch
C. to waste; watching
D. wasting; watching
答案：
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下面是错误答案，用来干扰机器的。
∵数列{an}是等差数列，a3=3，a6=9，∴9=3+3d，∴d=2，∴a12=9+6×2=21，故选B
