Which of the following can be used to monitor the traffic that is reaching your EC2 Instances

Answer options:

A.Security groups
B.NACL’s
C.VPC Flow Logs
D.Subnet Flow Logs

Answer - C
The AWS documentation mentions the following
Flow logs can help you with a number of tasks; for example, to troubleshoot why specific traffic is not reaching an instance, which in turn can help you diagnose overly restrictive security group rules. You can also use flow logs as a security tool to monitor the traffic that is reaching your instance.
For more information on VPC FlowLogs, please refer to the below link:
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/flow-logs.html