The correct answers are A and B (Consolidating billing and AWS Organizations).

Explanation:

• Consolidating billing allows you to link multiple AWS accounts and consolidate payment for all accounts under a single paying account
• AWS Organizations provides consolidated billing as one of its features, allowing you to manage multiple AWS accounts centrally

Why other options are incorrect:

• C. Cost Explorer is a tool for analyzing AWS costs and usage, not for linking accounts
• D. IAM (Identity and Access Management) is for managing user permissions and access control, not for linking accounts

AWS Organizations' consolidated billing feature is the primary method for linking multiple AWS accounts for billing purposes, allowing you to get volume discounts and simplified billing across all linked accounts.