如何使用LINQ合并列表中行中的数据？

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        List<List<int>> lists = new List<List<int>>
        {
            new List<int> { 1, 2, 3 },
            new List<int> { 4, 5, 6 },
            new List<int> { 7, 8, 9 }
        };

        var mergedList = lists.SelectMany(list => list);

        foreach (var num in mergedList)
        {
            Console.WriteLine(num);
        }
    }
}