For this question, I would suggest that you make a diagram to help you analyze it.
对这道题，我建议首先画一个图来帮助你分析。
I personally like to include return messages whenever a value will be returned, because I find the extra details make a sequence diagram easier to read.
我个人喜欢，无论什么时候返回一个值，都包括一个返回消息，因为我发现额外的细节使一个序列图变得更容易阅读。
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