Joe works for a company that has a traveling sales force. The company has asked Joe to research a way for the sales force to have real-time information on the availability of its salable products. The company has an intranet application that allows it to see up-to-the minute information. The company does not want to make this information public.

What should Joe recommend?
a. VPN
b. Firewall
c. Access control list
d. MDM policies