Which protocol should you include in the recommendation?

Your network contains an Active Directory domain named contoso.com.
All client computers run either Windows 7 or Windows 8.
Some users work from customer locations, hotels, and remote sites. The remote sites often
have firewalls that limit connectivity to the Internet.
You need to recommend a VPN solution for the users.
Which protocol should you include in the recommendation?

A.
PPTP

B.
SSTP

C.
IKEv2

D.
L2TP/IPSec