Option D is the correct answer. To optimize the cost of data processing, you can implement various strategies depending on the specific use case. Using spot instances for Amazon EMR clusters can help reduce the cost of EC2 instances by taking advantage of spare capacity in the AWS data centers. However, this may result in less predictable availability. Using reserved instances for Amazon RDS can provide cost savings over on-demand instances, especially for long-term workloads. AWS Lambda's pay-per-use pricing model can be cost-effective for data processing tasks with variable workloads, as you only pay for the actual compute time used. By combining these strategies, you can optimize the cost of data processing in your organization.