You have an application hosted in AWS, which sits on EC2 Instances behind an Elastic Load Balancer. You have added a new feature to your application and are now receiving users` complaints that the site has a slow response. Which of the below actions can you carry out to help you pinpoint the issue?

Answer options:

A.Use Cloudtrail to log all the API calls, and then traverse the log files to locate the issue.
B.Use Cloudwatch, monitor the CPU utilization to see the times when the CPU peaked.
C.Review the Elastic Load Balancer logs.
D.Create some custom Cloudwatch metrics which are pertinent to the key features of your application. 

Answer - D
Since the issue occurs after the new feature has been added, it could be relevant to the new feature.
Enabling Cloudtrail will monitor all the API calls of all services and will not benefit the cause.
The monitoring of CPU utilization will reverify that there is an issue but will not help pinpoint the issue.
The Elastic Load Balancer logs will also reverify that there is an issue but will not help pinpoint the issue.
For more information on custom Cloudwatch metrics, please refer to the below link:
http://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/publishingMetrics.html