核心问题
上海编《初中英语教科书》(8B, p.73)指出：“与时间状语从句一样，条件状语从句放在主句前面时要用逗号与主句分开。”但是，在该书的第94页上却出现了这样一个句子：When George was fourteen he became his father's helper. 在 when 从句之后没有用逗号，是否应看作错误？
词典解答
状语从句位于主句之前时，通常要用逗号与主句分开。但是，如果状语从句较短，也可以不使用逗号。例如：
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When he comes I will tell him to fetch the police. 他来的时候,我告诉他去叫警察。
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When he got up he felt dizzy. 他起床时感到头晕目眩。
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Though he was suffering great pain he walked home alone. 尽管他遭受着极大的疼痛，但他却自己走回了家。
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However, as soon as the great man came up he got off his horse, saying, "I see you've had bad luck, friend." 然而，这位大人物一走近，便立即下马，说：“朋友，我看你运气不佳。”
comma (逗号) 见 restrictive relative clause, where