Explanation:

Amazon SageMaker Ground Truth is specifically designed for data labeling tasks. It provides:

• Automatic labeling: Uses active learning and machine learning models to pre-label data
• Human labeling: Integrates with human workforce through Amazon Mechanical Turk or third-party vendors
• Workflow management: Creates labeling workflows and manages the labeling process
• Quality control: Includes built-in quality controls and verification mechanisms

For the healthcare startup working with X-ray images, SageMaker Ground Truth would be the ideal service because:

1. It can help automate the labeling process using ML models
2. It can supplement their limited internal annotators with external human labelers
3. It provides specialized workflows for medical imaging data
4. It ensures data privacy and security compliance for healthcare data

The other options serve different purposes:

• SageMaker Studio: Integrated development environment
• SageMaker Autopilot: Automated model building
• SageMaker Clarify: Model bias detection and explainability
• SageMaker Debugger: Model training monitoring and debugging
• SageMaker Model Monitor: Model performance monitoring in production