A:2π
B:4π
C:8π
D:83π
-This is ____________ useful book, I think.
-So it is, and it's ____________ unusual one.
成年人体内缺碘易患的病症是 ( )
如图所示,是甲、乙两物体做直线运动的位移﹣时间图象,则下列说法正确的是( )
解方程:x2﹣1=2(x+1).