问题
选择题
You used to wear glasses______. [ ]
A. Did you
B. do you
C. didn't you
D. don't you
答案
答案：C
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You used to wear glasses______. [ ]
A. Did you
B. do you
C. didn't you
D. don't you
答案：C
±2SD的范围内，其可信限是（）