The correct answer to the question “Which Microsoft Azure cloud security tool can an enterprise use for key management” is, option (d). Azure Key Vault. This is a service offered by Microsoft Azure, for securing secrets, which are stored and accessed frequently. This secret could be anything from a password, certificates, cryptographic keys.
If you wish to learn Microsoft Azure, check out the Azure Security certification course from Intellipaat. Also, have a look at the following YouTube video on Learn Azure.