How can the user configure this?

A user has setup Auto Scaling with ELB on the EC2 instances. The user wants to configure that whenever the
CPU utilization is below 10%, Auto Scaling should remove one instance. How can the user configure this?

A.
The user can get an email using SNS when the CPU utilization is less than 10%. The user can use
the desired capacity of Auto Scaling to remove the instance

B.
Use CloudWatch to monitor the data and Auto Scaling to remove the instances using scheduled
actions

C.
Configure CloudWatch to send a notification to Auto Scaling Launch configuration when the CPU
utilization is less than 10% and configure the Auto Scaling policy to remove the instance

D.
Configure CloudWatch to send a notification to the Auto Scaling group when the CPU Utilization is
less than 10% and configure the Auto Scaling policy to remove the instance

Explanation:
Amazon CloudWatch alarms watch a single metric over a time period that the user specifies and performs one
or more actions based on the value of the metric relative to a given threshold over a number of time periods.
The user can setup to receive a notification on the Auto Scaling group with the CloudWatch alarm when the
CPU utilization is below a certain threshold. The user can configure the Auto Scaling policy to take action for
removing the instance. When the CPU utilization is below 10% CloudWatch will send an alarm to the Auto
Scaling group to execute the policy.