A:as much a
B:books as much a
C:books as many a
D:as many books a
说一说在易拉罐运动过程中,有几种运动方式同时存在。( )
如图,在Rt△ABC中,∠BAC=90°,∠ABC的平分线BD交AC于点D,DE是BC的垂直平分线,点E是垂足.已知DC=5,AD=2,则图中长为21的线段有( )