Which strategy did the cloud provider use to mitigate the risk of security threats?

A cloud provider installs a virtual firewall on a hypervisor to reduce the scope of a security breach when there is already a network-based firewall deployed in the cloud environment.

Which strategy did the cloud provider use to mitigate the risk of security threats?
A . Trusted computing base
B . Defense-in-depth
C . Information assurance framework
D . Adaptive security

Answer: B