C#请求网页如何实现No-Cache方式

C#请求网页怎么实现No-Cache方式？
C++这么写的，那C#呢
HINTERNET hHttp = InternetOpenUrl(hSession, url, NULL, 0, INTERNET_FLAG_DONT_CACHE, 0);

C#怎样no-cache?
 req = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(url);
  res = (System.Net.HttpWebResponse)req.GetResponse();

[解决办法]

C# code

public static WebResponse GetResponseNoCache(Uri uri){        // Set a default policy level for the "http:" and "https" schemes.        HttpRequestCachePolicy policy = new HttpRequestCachePolicy(HttpRequestCacheLevel.Default);        HttpWebRequest.DefaultCachePolicy = policy;        // Create the request.        WebRequest request = WebRequest.Create(uri);        // Define a cache policy for this request only.         HttpRequestCachePolicy noCachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore);        request.CachePolicy = noCachePolicy;        WebResponse response = request.GetResponse();        Console.WriteLine("IsFromCache? {0}", response.IsFromCache);                    return response;}