What can be implemented to provide the highest level of protection from external attack?

A. Layering perimeter network protection by configuring the firewall as a screened host in a screened subnet behind the bastion host
B. Configuring the firewall as a screened host behind a router
C. Configuring the firewall as the protecting bastion host
D. Configuring two load-sharing firewalls facilitating VPN access from external hosts to internal hosts