Which of the following security features is associated with a Subnet in a VPC to protect against incoming traffic requests?

Answer options:

A.AWS Inspector
B.Subnet Groups
C.Security Groups
D.Network ACL

Answer – D
The AWS Documentation mentions the following:
A network access control list (ACL) is an optional layer of security for your VPC that acts as a firewall for controlling traffic in and out of one or more subnets. You might set up network ACLs with rules similar to your security groups in order to add an additional layer of security to your VPC. 
For more information on Network ACL, please visit the URL:
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_ACLs.html