题目

阅读下面短文，从短文后各题所给的四个选项（A、B、C和D），选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。 My sister, Cathy, who lives in Vancouver, sent me a package full of Christmas gifts. She told me that she had   36   it in advance to make sure it would arrive at my house weeks before the   37  . Christmas was drawing near, but no package arrived. Cathy checked the tracking number every   38   with Canada Post, and every evening she would call me to   39   if there was any sign of it on our end. The   40   如果数据x1，x2，…，xn的平均数是.x，方差是S2，则2x1+3，2x2+3，…，2xn+3的平均数和方差分别是（　　）A．.x和SB．2.x+3和4S2C．2.x+3和S2D．2.x+3和4S2+12S+9