轮到某人做某事（既可以是权力,有可能是义务.）
Now that I have finished buying,Tom,in his turn,should cook.
(Now that I have finished buying,it's Tom's turn to cook.
既然我已经买来了菜,就该由Tom来做菜了.
I bought the last CD in my turn.
轮到我的时候,我买走了最后一张CD.