已知圆锥的底面半径为1cm,母线长为3cm,则其全面积为 ( )
A:π
B:3π
C:4π
D:7π
—So it is. But it is expensive. It more than going by train.
家鸽体呈流线型,其意义在于( )
图中等温线a的值可能为( )