A:43
B:34
C:-34
D:-43
I will take a holiday with my family _______ I finish all the exams.
设随机变量ξ服从正态分布N(2,9),若P(ξ>c+1)=P(ξ<c﹣1),则c=____ .
修建了独特的水利工程“坎儿井”的省区是( )