Correct Answers: A and C.
The AWS Documentation mentions the following.
You can automatically increase the size of your Auto Scaling group when demand goes up and decrease it when demand goes down.
As the Auto Scaling group adds and removes EC2 instances, you must ensure that the traffic for your application is distributed across all of your EC2 instances.
The Elastic Load Balancing service automatically routes incoming web traffic across such a dynamically changing number of EC2 instances.
Option B is incorrect since Amazon GuardDuty is a threat detection service that continuously monitors for malicious activity and unauthorized behaviour.
Option D is incorrect since CloudWatch is a monitoring service.