黑心棉，即纤维性工业下脚料、医用纤维性废弃物、再生纤维状物质、废旧服装及其他废旧纤维制品等物质，这类劣质棉类制品没有经过消毒，可能成为细菌温床。那么黑心棉的危害有哪些呢？
I have a simple task. There are two classes : Ticket and Date. Ticket contains event, event place and event date which is a Date object. I also need to provide a move() method for Date object, so I us
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