改错：the boy who saw him just now won a prize in the sports meeting last month

改错：the boy who saw him just now won a prize in the sports meeting last month
改错：the boy who saw him just now won a prize in the sports meeting last month

改错：the boy who saw him just now won a prize in the sports meeting last month
The boy who saw him just now had won a prize in the sports meeting last month .
看见他的时间是刚才,而获奖时间是上个月.刚才已经是过去,而获奖是在看见他的过去发生的,所以“last month”是“过去的过去”,符合过去完成时的定义,故应用had won

我上个月看见的那个男孩在上刚才的运动会上获得奖

The boy who saw him judt now had won a prize in the sports meeting last month

我刚才看到的男孩他在上个月的运动会得了个奖