变量数列分析的原则。
参考答案:
①要注意总体单位的同质性;
②用组平均数补充总平均数;
③用次数分布补充总平均数;
④集中趋势与离散趋势测度相结合;
⑤注意一般与个别相结合。
—Look at the old lady in red. Is that Mrs. Lee?
—No, it _______ be her. She has gone to Canada. [ ]
A. won't
B. mustn't
C. can't
D. shouldn't
有一玻璃球在空气中称其重力为4.41牛顿,浸没在水中测力计示数为2.94牛顿,浸没在石油中测力计示数为3.30牛顿,求玻璃球和石油的密度.