You have large EC2 instances in your AWS infrastructure which you have recently set up. These instances carry out the task of creating JPEG files and store them on an S3 bucket and occasionally need to perform high computational tasks. After close monitoring, you see that the CPUs of these instances remain idle most of the time. 

Answer options:

A.Use Amazon glacier instead of S3.
B.Add additional large instances by introducing a task group.
C.Use T2 instances if possible.
D.Ensure the application hosted on the EC2 instances uses larger files on S3 to handle more load.

Answer – C
In this scenario, the problem is that the large EC2 instances are mostly remaining unused. Hence, the solution should be to use instances that can cost less but still be able to carry out occasional high computational tasks. 
T2 instances are Burstable Performance Instances that provide a baseline level of CPU performance with the ability to burst above the baseline. The baseline performance and ability to burst are governed by CPU Credits. T2 instances accumulate CPU Credits when they are idle and consume CPU Credits when they are active. T2 instances are the lowest-cost Amazon EC2 instance option designed to dramatically reduce costs for applications that benefit from the ability to burst to full core performance whenever required.
Option A is incorrect because there is no issue with the current use of S3.
Option B is incorrect because adding another large instance is, on the contrary, an expensive solution and would add to the existing cost.
Option C is CORRECT because T2 instances are cost-effective and also provide a baseline level of CPU performance with the ability to burst above the baseline whenever required.
Option D is incorrect because this option is not going to make efficient use of the current instances. It will not lower the cost of the architecture.
For more information on Instance types, please visit the below URL-
https://aws.amazon.com/ec2/instance-types/t2/