A System.Collections.Specialized.NameValueCollection that contains query name/value pairs associated with the request or, if this property has not been set or was set to null, a new instance of the System.Collections.Specialized.NameValueCollection class.
The WebClient.QueryString property contains a System.Collections.Specialized.NameValueCollection instance containing name/value pairs that are appended to the URI as a query string. The contents of the WebClient.QueryString property are preceded by a question mark (?), and name/value pairs are separated from one another by an ampersand (&).