What is the MOST efficient way to fulfill this request?

A developer has written a multi-threaded application that is running on a fleet of Amazon EC2 instances. The operations team has requested a graphical method to monitor the number of running threads over time.

What is the MOST efficient way to fulfill this request?
A . Periodically send the thread count to AWS X-Ray segments, then generate a service graph on demand
B . Create a custom Amazon CloudWatch metric and periodically perform a PutMetricData call with the current thread count.
C . Periodically log thread count data to Amazon S3. Use Amazon Kinesis to process the data into a graph.
D . Periodically write the current thread count to a table using Amazon DynarnoDB and use Amazon CloudFront to create a graph

Answer: D