C#实现过滤html标签并保留a标签的方法

  public static string ClearHtmlExceptA(string html) {    string acceptable = "a";    string stringPattern = @"</?(?(?=" + acceptable + @")notag|[a-zA-Z0-9]+)(?:/s[a-zA-Z0-9/-]+=?(?:(["",']?).*?/1?)?)*/s*/?>";    html = Regex.Replace(html, stringPattern, "");    html = Regex.Replace(html, @"[/t/n]", "", RegexOptions.IgnoreCase);    html = Regex.Replace(html, @"[/r]", "", RegexOptions.IgnoreCase);    //html = Regex.Replace(html, @"[/t/n/r/s]","",RegexOptions.IgnoreCase);    return html;  }