Which environment-specific configuration is used in AEM as a Cloud Service to store private API keys?

Which environment-specific configuration is used in AEM as a Cloud Service to store private API keys?
A . $[env:ENV_VAR_NAME]
B. $[env:SECRET_VAR_NAME]
C. $[secret:SECRET_VAR_NAME]
D. $[secret:ENV_VAR_NAME]

Answer: C

Explanation:

This syntax allows the developer to reference a secret variable that is stored in the Cloud Manager UI under Environment Details > Variables. The secret variable name must start with a lowercase letter and can contain alphanumeric characters and underscores.

Reference: https://experienceleague.adobe.com/docs/experience-manager-cloud-service/implementing/deploying/configuring-osgi.html?lang=en#environment-specific-configuration