Jim doesn't ____ ____ at school.
We have been in the school ______ three years ago and Mrs. Lee Has taught us English_______ three years.
如下图所示,将若干个点摆成三角形图案,每条边(包括两个端点)有n(n>1,n∈N*)个点,相应的图案中总的点数记为an,则9a2a3+9a3a4+9a4a5+...+9a2013a2014等于( )
对下列实验中出现异常情况的原因分析,不合理得是( )