试讨论货币作为流通手段、价值尺度和储藏手段的职能。你认为某些可再生性商品，如可可豆，能成为好的货币吗？为什么？ Discuss the role of money as a medium of exchange，unit of account，and store of value．Do you think that some reproducible commodity，for example，cocoa seeds，would make a good money？Why？