问题
选择题
While she _________ TV in the sitting room, the bell________.
A．watches, rings
B．is watching, rang
C．was watching, rang
D．watched, was ringing
答案
答案：C
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While she _________ TV in the sitting room, the bell________.
A．watches, rings
B．is watching, rang
C．was watching, rang
D．watched, was ringing
答案：C
=23020，
=540，n=15，∑XiYi=3413，=0.0285，∑(Yi-Y)2=97.37，∑(Yi-Y)2=113.33。
=-4.2769+0.2538Xi，回归系数表示年龄每增加1岁，缺勤增加0.2538天
，回归系数表示年龄每增加1岁，缺勤减少4.2769天