gistfile1.cs

using System;

namespace Test
{
    using System.Linq.Expressions;

    class Program
    {
        static void Main(string[] args)
        {
            var a = new A();
            var b = new B();

            Console.WriteLine(a.GetPropertyName(x => x.B));
            Console.WriteLine(b.GetPropertyName(x => x.C));


            Console.WriteLine("Press Enter to exit...");
            Console.ReadLine();
        }
    }

    static class Extensions
    {
        public static string GetPropertyName<T1, T2>(this T1 source, Expression<Func<T1, T2>> expression)
            where T1 : A
        {
            var propertyExpression = expression.Body as MemberExpression;

            var name = propertyExpression.Member.Name;

            return name;
        }
    }

    class A
    {
        public string B { get; set; }
    }

    class B : A
    {
        public string C { get; set; }
    }
}