检查一个门框是否为矩形,下列方法中正确的是( )
A:测量两条对角线,是否相等
B:测量两条对角线,是否互相平分
C:测量门框的三个角,是否都是直角
D:测量两条对角线,是否互相垂直
The little girl is not to take care of herself. So her mother looks after her.
7km30m=____km