Which of the following is a limitation of the Elastic Fabric Adapter (EFA)?

Answer options:

A.EFA provides all of the functionality of an ENA (Elastic Network Adapter).
B.The EFA must be a member of a security group that allows only inbound traffic to the security group itself.
C.OS-bypass functionality is supported by EFA, not by ENA.D.OS-bypass capabilities of EFAs are not supported on Windows instances.

Correct Answer: B and D
An Elastic Fabric Adapter (EFA) is a network device that you can attach to your Amazon EC2 instance to accelerate High-Performance Computing (HPC) and machine learning applications. 
Option A is incorrect because it is a true feature of EFA. An EFA is an Elastic Network Adapter (ENA) with added capabilities. It provides all of the functionality of an ENA, with additional OS-bypass functionality. 
Option B is correct because it is one of the limitations of EFA (Elastic Fabric Adapter).
Option C is incorrect because OS-bypass functionality is supported only by EFA.Option D is correct because it is also a limitations. The OS-bypass capabilities of EFAs are not supported on Windows instances. If you attach an EFA to a Windows instance, the instance functions as an Elastic Network Adapter, without the added EFA capabilities.
Reference:
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/efa.html