using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        // Note that this is going to be a list that is generated based on your checkboxes.

        // I just couldn't replicate it easily in a test environment, so I generated these lists

        // based of the values that you provided.

        var location = new[]

        {

          "NearMainGate", 

          "NearMP5WestGate"

        };

        var modifier = new[]

        {

          "WindDir", 

          "WindVel"

        };

        var lambdaResult = modifier.SelectMany(s => location.Select(l => string.Format("{0}{1}{2}", "C.", s, l)));

        var queryResult =

            from m in modifier

            from l in location

            select string.Format("{0}{1}{2}", "C.", m, l);

        Console.WriteLine("Lambda result");

        lambdaResult.ToList()

                    .ForEach(Console.WriteLine);

        Console.WriteLine();

        Console.WriteLine("Query result");

        queryResult.ToList()

                   .ForEach(Console.WriteLine);

    }

}