Porch adjust measures to local conditions, but can small; Because the person makes appropriate, but Jian Kefan, but absolutely cannot dispensable, ought to ask according to it, serious processing.
玄关因地制宜，可大可小；因人制宜，可简可繁，但绝不能可有可无，应当根据它的要求，认真处理。
Zhao Jian: Because there must be some time gap between each train. If the time difference is too small, they will crash. So, you cannot operate more trains on it.
赵坚：因为每辆列车之间必须有一些时间间隔，如果间隔过小，列车就会相撞，所以不能运行再多的列车。
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