他掩护他们小组撤退，而且因为这一行动而受到表扬。

[误] He was praised for the act of covering the retreat of his group.

[正] He was praised for the action of covering the retreat of his group.

注： act 指具体、短暂和简单的行为，它侧重于效果，如：He was caught in the act of stealing(他正行窃时被当场抓获)。而 action 指抽象、持续和复杂的行为，它侧重于行为的过程及作用。