Option A is incorrect because it's not a cost-effective solution
Option B is incorrect because it's not in the native Azure solution
Options C is correct because as part of adding an extra layer of authentication for critical operations, you're prompted to enter a security PIN when you perform Stop Protection with Delete data and Change Passphrase operations, Option D is correct because enabling this security feature protects your backup from accident and malicious deletion, adding a layer of security.
Reference:
https://docs.microsoft.com/en-us/azure/security/fundamentals/backup-plan-to-protect-against- ransomware