c# capitalize first letter of each word in a string

public static class StringExtension
{
    public static string CapitalizeFirst(this string s)
    {
        bool IsNewSentense = true;
        var result = new StringBuilder(s.Length);
        for (int i = 0; i < s.Length; i++)
        {
            if (IsNewSentense && char.IsLetter(s[i]))
            {
                result.Append (char.ToUpper (s[i]));
                IsNewSentense = false;
            }
            else
                result.Append (s[i]);

            if (s[i] == '!' || s[i] == '?' || s[i] == '.')
            {
                IsNewSentense = true;
            }
        }

        return result.ToString();
    }
}

string s = "THIS IS MY TEXT RIGHT NOW";
s = CultureInfo.CurrentCulture.TextInfo.ToTitleCase(s.ToLower());

string s = "THIS IS MY TEXT RIGHT NOW";

s = System.Threading.Thread.CurrentThread.CurrentCulture.TextInfo.ToTitleCase(s.ToLower());