react这个错是什么意思，要怎么解决

Question

上面的代码效果出来了，但是报了下面这个错，刚刚接触react，有点儿不理解，还请各位指教：
Warning: Each child in an array or iterator should have a unique "key" prop. Check the render method of Comment. See https://fb.me/react-warning-keys for more information.