答案非常简单：
Mary is good at singing.
= Mary does well in singing.
即：be good at = do well in 在...好/擅长于...
如果你满意我的答案,敬请点击“选为满意回答” ,只有两格大哥，你这样我也会好吧！如果只有两空，则最好填上：sings wellMary sings well. 玛丽唱得很好/棒。 如果你满意我的答案，敬请点击“选为满意回答” ，谢谢！