Your company has a set of resources defined in AWS. They have a particular budget per month and want to be notified if they are coming close to that budget regarding the usage costs for the underlying resources. How could you achieve this requirement?

Answer options:

A.Create an alarm based on the costing metrics for a collection of resources.
B.Create a billing alarm from within Cloudwatch.
C.Create a billing alarm from within Cost Explorer.
D.Create a billing alarm from within IAM.

Correct Answer: B
This is given in the AWS Documentation.
You can monitor your estimated AWS charges using Amazon CloudWatch. When you enable the monitoring of estimated charges for your AWS account, the estimated charges are calculated and sent several times daily to CloudWatch as metric data.
Option A is invalid because you cannot get cost as a metric specifically in Cloudwatch.
Options C and D are invalid because the billing alarm needs to be created from Cloudwatch.
For more information on monitoring charges with AWS Cloudwatch, please refer to the below URL-
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/monitor_estimated_charges_with_cloudwatch.htm