The security team at Certkiller Inc. is working on private VLANs.
What are private VLANs?

A.
Private VLANs are tools that allow segregating traffic at Layer 3, turning broadcast segments into non-broadcast, multi-access-like segments.

B.
Private VLANs are tools that allow segregating traffic at Layer 2, turning non-broadcast, multi-access-like segments into broadcast segments.

C.
Private VLANs are tools that allow segregating traffic at Layer 3, turning non-broadcast, multi-access-like segments into broadcast segments.

D.
Private VLANs are tools that allow segregating traffic at Layer 2, turning broadcast segments into non-broadcast, multi-access-like segments

Explanation:

Within an existing VLAN, private VLANs provide some added security to specific network applications. Private VLANs work by limiting which ports within a VLAN can communicate with other ports in the same VLAN. Isolated ports within a VLAN can communicate only with promiscuous ports. Community ports can communicate only with other members of the same community and promiscuous ports. Promiscuous ports can communicate with any port. This is an effective way to mitigate the effects of a single compromised host.
Reference: Safe White papers; Page 5
SAFE: Extending the Security Blueprint to Small, Midsize, and Remote-User Networks