You need to allow users to access the application by using their Google accounts

You administer an Access Control Service namespace named contosoACS that is used by
a web application. ContosoACS currently utilizes Microsoft and Yahoo accounts. Several
users in your organization have Google accounts and would like to access the web
application through ContosoACS.
You need to allow users to access the application by using their Google accounts. What
should you do?

A.
Register the application directly with Google.

B.
Edit the existing Microsoft Account identity provider and update the realm to include
Google.

C.
Add a new Google identity provider.

D.
Add a new WS-Federation identity provider and configure the WS-Federation metadata to
point to the Google sign-in URL.

Explanation:
http://msdn.microsoft.com/en-us/library/azure/gg185976.aspx