单项选择题 设总体X的数学期望与方差存在,是X的样本,则可以作为的无偏估计的是( ) A. 当已知时, B. 当已知时, C. 当未知时, D. 当未知时,

单项选择题 Under fixed exchange rates, which one of the following statements is the MOST accurate?

单项选择题 The four dimensions of multi-dimensional empathy include emotional, cognitive, moral and behavioral empathy, among which behavioral empathy refers to the ability to recognize and understand the views and emotions of others.  A、正确 B、错误