How do I replace multiple spaces with a single space in C#?

Example "1 2 3  4    5" would be : "1 2 3 4 5"?

RegexOptions options = RegexOptions.None;
Regex regex = new Regex(@"[ ]{2,}", options);
tempo = regex.Replace(tempo, @" ");

myString = Regex.Replace(myString, @"s+", " ");

string xyz = "1   2   3   4   5";
xyz = string.Join( " ", xyz.Split( new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries ));

while(str.Contains("  ")) str = str.Replace("  ", " ");

myString = Regex.Replace(myString, " {2,}", " ");

myString = Regex.Replace(myString, @"s+", " ", RegexOptions.Multiline);

string s = Regex.Replace (
    "   1  2    4 5",
    @"[ ]{2,}",
    " "
    );

static class StringExtensions
{
    public static string Join(this IList<string> value, string separator)
    {
        return string.Join(separator, value.ToArray());
    }
}

//...

string s = "     1  2    4 5".Split (
    " ".ToCharArray(),
    StringSplitOptions.RemoveEmptyEntries
    ).Join (" ");

public static string Join<T>(this IEnumerable<T> source, string separator)
{
    return string.Join(separator, source.Select(e => e.ToString()).ToArray());
}

//...

string s = "     1  2    4 5".Split (
    " ".ToCharArray(),
    StringSplitOptions.RemoveEmptyEntries
    ).Join (" ");

while (str.IndexOf("  ") != -1)
  str = str.Replace("  ", " ");