The 140 character limit is necessary only because text messages, one of Twitter's primary source channels, are similarly constrained.

（140 字符的限制完全来自文本消息，它是 Twitter 的主要来源渠道，并受到类似的限制）。

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Examine all allusions found within the text by tracing their roots to the primary text or source, if possible.

精细研读文本中的所有用典，如有可能，对用典要刨根问底。

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