You administer a SharePoint 2013 environment. You use iframes to display dynamic content from other sites.
You need to allow contributors to insert iframes into pages on the site from any external domain. What should
you configure?

A.
HTML field security

B.
site collection app permissions

C.
site permissions

D.
portal site connections

E.
site app permissions

Explanation:
http://www.learningsharepoint.com/2012/11/24/how-to-use-iframes-in-sharepoint-2013/