experience既可以作为可数名词又可以作为不可数名称
当表示“经验”的时候是不可数的，如
He is a good teacher with much experience
He has a lot ot experience in the rearch.在这个研究上他 很有经验。
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当表示“经历，经历的事”是可数的，如
Travelling in the USA is really a great experience.
He has a lot of experiences of travelling.他有很多旅游的经历。
