A:Al2O3
B:Fe2O3
C:SiO2
D:CaO
如图,顺次连接圆内接矩形各边的中点,得到菱形ABCD,若BD=8,DF=4,则菱形ABCD的边长为多少?
下列各项不能说明海陆处在不断的运动和变化中的是( )
Try to ________ half an hour each day for keeping a diary, and you'll achieve distinction in writing.