凡尔赛—华盛顿体系最先遭到破坏的历史事件是

A．日本制造九一八事变

B．德国撕毁《凡尔赛和约》

C．德军开进莱茵不设防区

D．日本和德国退出国联

On a ship，how many ring buoys are required to have a buoyant line attached?（）

A.One ring life buoy

B.One ring life buoy on each side of the ship

C.Three ring life buoys

D.Two ring life buoys on each side of the ship