Answer: Install the Amazon CloudWatch agent and configure memory metric collection on the EC2 instances., Configure AWS Compute Optimizer in the AWS account to receive findings and optimization recommendations.

C: **Install the Amazon CloudWatch agent and configure memory metric collection on the EC2 instances.** This step is crucial because by default, Amazon CloudWatch does not provide detailed memory utilization metrics for EC2 instances. Installing and configuring the CloudWatch agent allows the collection of memory metrics along with CPU and network metrics. This detailed data is necessary to evaluate the performance of EC2 instances accurately and identify any under or over-utilization of resources, which is critical for cost optimization and appropriate instance sizing. D: **Configure AWS Compute Optimizer in the AWS account to receive findings and optimization recommendations.** AWS Compute Optimizer provides tailored recommendations to optimize the performance and cost of your AWS resources, including EC2 instances. It utilizes machine learning to analyze the historical utilization metrics (CPU, memory, and network) gathered by sources like CloudWatch. Based on this analysis, it generates recommendations on the right-sizing of your instances, suggesting larger or smaller instances or different instance types that may be more cost-effective while meeting performance requirements. This tool is integral to ensuring that EC2 instances are both cost-optimized and appropriately sized for their workloads.

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