CRM person and oprtunity entity webservices

Hi All,

we have a small section of opportunity entity inside person entity in a form called"new prospect students".

How can I point my webservices code to that section like

account.Attributes["opportunity->prorgam-name????"] = new EntityReference("?????", new Guid("232ad52b-a648-e311-97b2-005056ae44f4"));

Thanks alot