Explanation:

✅ C. Data Migration Assistant (DMA) tool for analyzing data format and compatibility
The Data Migration Assistant (DMA) is specifically designed to help assess whether legacy data is formatted correctly, complete, and compatible with Salesforce data structures. It helps identify data quality issues, field mismatches, and transformation needs before migration begins. This makes DMA the most strategic choice for assessing data readiness and planning remediation before any import or mapping activities.

References:
🔗 Salesforce Data Migration Guide

❌ A. Salesforce Data Loader for bulk data imports and mapping
Data Loader is a powerful tool for importing and exporting large volumes of data, but it does not assess data quality or readiness. It assumes your data is already clean and correctly formatted. Using it without assessment could result in failed uploads or data integrity issues.

❌ B. Data Quality Rules within Salesforce highlighting inconsistencies and missing information
These rules only work once data is inside Salesforce. They can help identify missing or malformed records post-import, but they don’t assess data readiness in the source system. Therefore, they’re useful after migration, not before it.

❌ D. Custom Apex code scripts developed to assess and clean legacy data for migration
While Apex scripts can be written for assessment or cleaning, this requires custom development effort, introduces complexity, and lacks the out-of-the-box analytics provided by tools like DMA. It’s more of a fallback option when standard tools aren’t sufficient, not a preferred first step.