23．In view of lacking preparations for the competition and not wanting to lose face, Johnson eventually decided to _____．

A．drop in

B．drop off

C．drop back

D．drop out

成人脊髓下末端一般平对（）

A.第1腰椎下缘

B.第2腰椎下缘

C.第1骶椎下缘

D.第2骶椎下缘

E.骶管裂孔