which Microsoft .NET class should you use to send and receive data by using a web service?

You are developing a game for Windows Phone 7.
To maintain a high score list on a web server, which Microsoft .NET class should you use to
send and receive data by using a web service?

A.
PacketReader

B.
NetworkSession

C.
UdpClient

D.
HttpWebRequest

Explanation:
http://msdn.microsoft.com/en-us/library/hh221581.aspx