According to the Citrix Virtual Apps and Desktops 7 Administration On-Premises and in Citrix Cloud course, the Responder policy expression determines which requests are redirected by the Responder action. The expression http.REQ.URL.EQ("/") matches only the requests for the root page, and not any other pages. This prevents the redirection loop that occurs when the Responder action expression is also the root page. The other options are incorrect because they either match all requests or none.