VOA慢速英语:American History: German Sub Attacks Push Wilson Into War

cut off切〔隔〕断, 阻碍

例句：Our troops cut off the enemy's retreat.
      我们的军队切断了敌人的退路。

2.The extra strength they gave the Allies would play a major part in helping defeat Germany.

play a  part起作用

例句：Recent structural changes also play a part.
      最近的结构性变化也扮演了重要角色。