a sitting duck可不是“坐着的鸭子”，而真实含义是“瓮中之鳖;容易被打击的对象;易捕获的猎物”。

【例句】
Without our help, you would be a sitting duck.
要不是我们帮忙，你早成瓮中之鳖了。

With their bullets all gone, the soldiers were sitting ducks for the enemy.
子弹耗尽，士兵们成了敌人的瓮中之鳖。