The correct answer is B. Data explorer. Microsoft Learn states that Data explorer in Microsoft Purview shows a current snapshot of items that have been classified as a sensitive information type in your organization. Microsoft's sensitive information type documentation specifically lists examples such as social security numbers and credit card numbers, which means Data explorer is the appropriate portal feature for identifying files and emails that contain those data types. Data explorer is designed to help administrators see where sensitive data exists across supported Microsoft 365 locations.

The other options are less appropriate for this task. Information Protection reports focus more broadly on label and protection reporting. Information Protection policies are for configuring classification and protection behavior, not for finding existing files and emails containing SSNs or credit card numbers. Activity explorer is primarily used to review user and policy-related activities, such as label changes or DLP events, rather than to provide the direct sensitive-data inventory view requested here. Since the question asks to identify the files and emails containing specific sensitive information types, Microsoft's documented answer is Data explorer.