There are some health problems that，when in time，can become bigger ones later on. (2013·浙

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(答案→)A. not treated
B. not being treated
C. not to be treated
D. not having been treated
解析：
句意为：有些健康问题，如果不及时处理，以后会变得更严重。when not treated in time为插入语，在本句中为时间状语从句，把that can bee bigger ones later on这个定语从句给隔开了。when引导时间状语从句时，可以出现省略的现象，但必须满足两个条件：首先，时间状语从句中的主语必须和主句主语一致；其次，从句中含有be动词。本句补充完整的状语从句为：when they are not treated in time，其他选项形式不对。故答案为A项。