[誤] 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 指具體、短暫和簡單的行為,它側重于效果,如:He was caught in the act of stealing(他正行竊時被當場抓獲)。而 action 指抽象、持續(xù)和復雜的行為,它側重于行為的過程及作用。