Get trending topics of twitter api with C# - api

Question

I get "401 Unauthorized" error while trying to get the current trends using the twitter api but the below code work fine if I try to get some other response like user_timeline,available,tweets. Below is my code please tell me where iam wrong.
var oauth_token = "****";
var oauth_token_secret = "****";
var oauth_consumer_key = "****";
var oauth_consumer_secret = "****";
// oauth implementation details
var oauth_version = "1.0";
var oauth_signature_method = "HMAC-SHA1";
// unique request details
var oauth_nonce = Convert.ToBase64String(
new ASCIIEncoding().GetBytes(DateTime.Now.Ticks.ToString()));
var timeSpan = DateTime.UtcNow
- new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
var oauth_timestamp = Convert.ToInt64(timeSpan.TotalSeconds).ToString();
// message api details
var status = "Updating status via REST API if this works";
//var resource_url = "https://api.twitter.com/1.1/statuses/user_timeline.json";
//var resource_url = "https://api.twitter.com/1.1/search/tweets.json";
// var resource_url = "https://api.twitter.com/1.1/trends/place.json";
var resource_url = "https://api.twitter.com/1.1/trends/available.json";
//var screen_name = "screenname";
var query = "india";
var id = "1";
// create oauth signature
//var baseFormat = "oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}" +
// "&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}&screen_name={6}";
//var baseFormat = "oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}" +
//"&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}&q={6}";
var baseFormat = "oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}" +
"&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}&id={6}";
var baseString = string.Format(baseFormat,
oauth_consumer_key,
oauth_nonce,
oauth_signature_method,
oauth_timestamp,
oauth_token,
oauth_version,
id);
baseString = string.Concat("GET&", Uri.EscapeDataString(resource_url), "&", Uri.EscapeDataString(baseString));
var compositeKey = string.Concat(Uri.EscapeDataString(oauth_consumer_secret),
"&", Uri.EscapeDataString(oauth_token_secret));
string oauth_signature;
using (HMACSHA1 hasher = new HMACSHA1(ASCIIEncoding.ASCII.GetBytes(compositeKey)))
{
oauth_signature = Convert.ToBase64String(
hasher.ComputeHash(ASCIIEncoding.ASCII.GetBytes(baseString)));
}
// create the request header
var headerFormat = "OAuth oauth_nonce=\"{0}\", oauth_signature_method=\"{1}\", " +
"oauth_timestamp=\"{2}\", oauth_consumer_key=\"{3}\", " +
"oauth_token=\"{4}\", oauth_signature=\"{5}\", " +
"oauth_version=\"{6}\"";
var authHeader = string.Format(headerFormat,
Uri.EscapeDataString(oauth_nonce),
Uri.EscapeDataString(oauth_signature_method),
Uri.EscapeDataString(oauth_timestamp),
Uri.EscapeDataString(oauth_consumer_key),
Uri.EscapeDataString(oauth_token),
Uri.EscapeDataString(oauth_signature),
Uri.EscapeDataString(oauth_version)
);
// make the request
ServicePointManager.Expect100Continue = false;
//var postBody = "screen_name=" + Uri.EscapeDataString(screen_name);
//var postBody = "q=" + Uri.EscapeDataString(query);
var postBody = "id=" + Uri.EscapeDataString(id);
// resource_url += "?" + postBody;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(resource_url);
request.Headers.Add("Authorization", authHeader);
request.Method = "GET";
request.ContentType = "application/x-www-form-urlencoded";
WebResponse response = request.GetResponse();
string responseData = new StreamReader(response.GetResponseStream()).ReadToEnd();
Console.ReadLine();