关于Jefferson骨折，下列说法不正确的是（）。

A.Jefferson又称寰椎前后弓骨折

B.X线很难发现骨折线，常需行CT检查

C.可以并发枢椎齿状突骨折

D.治疗以手法复位内固定为主

E.多为垂直暴力所致

When a vessel signals her distress by means of a gun or other explosive signal，the firing should be at intervals of approximately（）.

A.10 minutes

B.1 minute

C.1 hour

D.3 minutes