You used to wear glasses______. [ ]
A. Did you
B. do you
C. didn't you
D. don't you
答案:C
当某测定值在±2SD的范围内,其可信限是()
A.68%
B.99%
C.没有明确的规定
D.95%
E.90%
简述霍兰德“职业六边形”理论的基本内容。