均数的抽样研究中，欲使样本均数推断总体均数的可靠性大，哪项必然小（）
A．cv
B．s
C．Sx
D．R
E．t
参考答案：C
Kangkang has ____ many good friends ____ he is very happy. [ ]
A. so, that
B. such, that
C. not, until
D. not, but
QR技术成功实施的条件
