题目

完形填空（共20小题；每小题1.5分，满分30分） 请阅读下面短文，掌握其大意，然后从36~55各题所给的四个选项（A、B、C和D）中，选出最佳选项，并在答题卡上将该选项的标号涂黑。 It was December 22. The bitter wind swept the countless snowflakes(雪花) across my front yard. My dad was there sweeping the  36 . His nose was red as a cherry. With every breath he took, a white puff escaped  37  the air. Inside, my mother was _38_the last of the boxes.  39  I entered the front door, the thought that after today I wouldn’t enter th老师布置了一道计算题：计算(a2+b2a2-b2-a-ba+b)÷2ab(a-b)(a+b)2-(a+b)的值，其a=2012，b=2013．小明把a、b错抄成a=2013，b=2012，但老师发现他的答案还是正确的，你认为这是怎么回事？说说你的理由．