C#後台給某網址傳遞參數，並接收返回值

[csharp]
string url = string.Format( 
    "http://bms.hichina.com/sms_gateway/sms_api?" 
    + "user_id={0}&password={1}&mobile_phone={2}" 
    + "&msg={3}&send_date={4}&subCode={5}" 
, string.Empty //用戶id  
, string.Empty //密碼  
, string.Empty //電話號碼  
, Server.UrlEncode(string.Empty) //短信消息  
, Server.UrlEncode(string.Empty) //發送日期  
, string.Empty //企業號  
); 
System.Net.WebClient client = new System.Net.WebClient(); 
string reply = client.DownloadString(url); 
Response.Write(reply);