Comments by Clifford Nelson (Top 200 by date)

static void Main(string[] args)
        {
            List<carowner> owners = new List<carowner>()
            {
                new CarOwner(){Name="Hari", Gender="Male",Age=23,      Cars= new List<car>(){new Car(){Name="Ambassador", Type="Heavy"},new Car(){Name="Maruti", Type="Light"}}},
                new CarOwner(){Name="Ruchira", Gender="Female",Age=18, Cars= new List<car>(){new Car(){Name="Sumo", Type="Heavy"}}},
                new CarOwner(){Name="Shyam", Gender="Male",Age=45,       Cars= new List<car>() },
                new CarOwner(){Name="Rakesh", Gender="Male",Age=40,      Cars= new List<car>(){new Car(){Name="Renault", Type="Heavy"},new Car(){Name="Pageiro", Type="Heavy"}}},
                new CarOwner(){Name="Sarmistha", Gender="Female",Age=40, Cars= new List<car>(){new Car(){Name="Innova", Type="Heavy"},new Car(){Name="Maruti", Type="Light"},new Car(){Name="Eon",Type="Light"},new Car(){Name="Jeep",Type=""}}},
                new CarOwner(){Name="Aliah", Gender="Female",Age=64,     Cars= new List<car>(){new Car(){Name="Bolero", Type="Heavy"},new Car(){Name="Hyundai", Type="Light"}}},
            };

            var results = owners.GroupBy(o => o.Gender, o => o.Cars, (key, g) =>
                new 
                {
                    Gender = key,
                    Name = g.SelectMany(cars => cars)
                    .Select(car => car.Name).Distinct().OrderBy(k => k).ToList()
                });

            foreach (var result in results)
            {
                Console.Write(result.Gender + ": " + string.Join(", ", result.Name.ToArray()));
                Console.WriteLine();
            }
            Console.ReadLine();
        }