AWS Cost Explorer and AWS Compute Optimizer are the two services that can identify rightsizing opportunities for Amazon EC2 instances:

• AWS Cost Explorer: Helps analyze costs and usage patterns, allowing you to identify underutilized EC2 instances that could be rightsized to save costs.
• AWS Compute Optimizer: Specifically designed to recommend optimal AWS resources for your workloads, including EC2 instance types, based on utilization metrics.

The other options are not designed for rightsizing:

• AWS Billing Conductor: Manages billing and cost allocation, not rightsizing recommendations
• Amazon CodeGuru: Focuses on code quality and performance optimization for applications
• Amazon SageMaker: A machine learning service, not related to infrastructure rightsizing