十九世纪中晚期，思想领域的重大新现象是什么？
参考答案：社会主义思想广泛兴起征，马克思主义产生。
—Why were you so late this morning?
—I _____ in heavy traffic for an hour on the way here.
A．have been caught
B．have caught
C．had caught
D．was caught
来自同一总体的两个样本中，（）小的哪个样本均数估计总体均数时更可靠.
A.标准差
B.标准误
C.变异系数
D.离均差平方和
