A:Ba2+,OH﹣,H+
B:H+,Na+, CO32−
C:N H4+ ,Na+,S O42−
D:Cu2+,N O3− ,OH﹣
如图,⊙O的弦AB=8,OE⊥AB于点E,且OE=3,则⊙O的半径是 ( )
Look at the elephant. It's so big.