关于状语从句的省略
Before you are operated on,you mustn't eat anything.
可以变为Before being operated on,you mustn't eat anything.
When the museum is finished,the museum will be open to the public.
为什么不能变为When being finished
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什么时候V-ing 可以变为 being done
如 After graduating from university,he went to China to study Chinese.可不可以