单项选择题

A.rid=2[Rb+rbe+(1+β)Rp/2];ro≈2Rc
B.rid=[Rb+rbe+(1+β)Rp/2];ro≈Rc
C.rid=[Rb+rbe+(1+β)Rp/2];ro≈2Rc
D.rid=1/2[Rb+rbe+(1+β)Rp/2];ro≈1/2Rc