單項(xiàng)選擇題凡是在()范圍內(nèi)的質(zhì)量差異都是偶然性因素作用的結(jié)果,屬于正常范圍。

A.(%26mu;-%26sigma;)~(%26mu;+%26sigma;)
B.(%26mu;-2%26sigma;)~(%26mu;+2%26sigma;)
C.(%26mu;-3%26sigma;)~(%26mu;+3%26sigma;)
D.都不是