[C# Lambda] 依資料Group某欄位數量

C# lamba List<object>, 其中object class有4個欄位, 分別為A,B,C,D, 其中A,B,C為string, D為int, 如何將A,B,C為條件進行Group by取得加總D的結果

class Program

{

    static void Main()

    {

        List<MyObject> objects = new List<MyObject>

        {

            new MyObject { A = "A1", B = "B1", C = "C1", D = 10 },

            new MyObject { A = "A1", B = "B1", C = "C2", D = 20 },

            new MyObject { A = "A2", B = "B2", C = "C1", D = 30 },

            new MyObject { A = "A2", B = "B2", C = "C2", D = 40 },

            new MyObject { A = "A2", B = "B3", C = "C3", D = 50 }

        };

        var groupedObjects = objects

            .GroupBy(obj => new { obj.A, obj.B, obj.C })

            .Select(group => new

            {

                group.Key.A,

                group.Key.B,

                group.Key.C,

                SumD = group.Sum(obj => obj.D)

            });

        foreach (var group in groupedObjects)

        {

            Console.WriteLine($"A: {group.A}, B: {group.B}, C: {group.C}, SumD: {group.SumD}");

        }

    }

}

class MyObject

{

    public string A { get; set; }

    public string B { get; set; }

    public string C { get; set; }

    public int D { get; set; }

}