Function IsAlphabetic - Practice Exercises C# Sharp

using System;
public class FunctionIsAlpha
{
    public static bool IsAlpha(char simbolo)
    {
        if ((simbolo >= 'a') && (simbolo <= 'z'))
            return true;

        if ((simbolo >= 'A') && (simbolo <= 'Z'))
            return true;

        return false;
    }

    public static bool IsAlpha2(char simbolo)
    {
        simbolo = Char.ToLower(simbolo);
        if ((simbolo >= 'a') && (simbolo <= 'z'))
            return true;

        return false;
    }

    public static bool IsAlpha3(char simbolo)
    {
        simbolo = simbolo.ToString().ToLower()[0];
        if ((simbolo >= 'a') && (simbolo <= 'z'))
            return true;

        return false;
    }

    public static bool IsAlpha4(char simbolo)
    {
        string validas = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqwrstuvwxyz";
        if (validas.Contains(simbolo))
            return true;

        return false;
    }

    public static void Main()
    {
        Console.WriteLine(
         IsAlpha('w'));
        Console.WriteLine(
         IsAlpha('2'));
    }
}