WCF - let the client choose the return format

[djsbrasil]

I'm trying to learn some WCF on my own. I have C#/ASP.net knowledge but I am new to WCF. I am using Visual Studio 2010 to develop some apps while I learn.I developed a small web service which acts as the backend for a TODO/Task manager where a user can create/delete/edit new events; it's all very simple and basic.My questions are the following:[*]Is there a way to let the client choose the return format he wants (e.g. xml/json/rdf) without writing new operation contracts? [*]How can I see on the client the exact message the Web Service sends to me (so that I can check if it's for instance a json representation or an xml message).