Combine the ten numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 into three three-digit numbers and one single-digit number, and make the sum of these four numbers 999. We require the largest What is the largest three-digit number if the three-digit number is as small as possible?
将0、1、2、3、4、5、6、7、8、9十个数字，组成三个三位数、一个一位数，并且使这四个数之和为999，我们要求最大的三位数尽可能小，则这个最大的三位数是多少．
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