过滤字符串中的html标签

public static string ClearHtml(string html)
        {
           if(string.IsNullOrEmpty(html))
            {
                return "";
            }
            //去除a标签
            html = Regex.Replace(html, @"<a\s*[^>]*>", "", RegexOptions.IgnoreCase);
            html = Regex.Replace(html, @"</a>", "", RegexOptions.IgnoreCase);
            //去除span标签
            html = Regex.Replace(html, @"<span\s*[^>]*>", "", RegexOptions.IgnoreCase);
            html = Regex.Replace(html, @"</span>", "", RegexOptions.IgnoreCase);
            //去除所有的样式
            html = Regex.Replace(html, @"\sstyle=""([^"";]+;?)+""", "", RegexOptions.IgnoreCase);

            //去除所有的html标签
            html = Regex.Replace(html, @"<[^>]*>|&nbsp;", "", RegexOptions.IgnoreCase);
            return html;
        }