The recommended practice for securely storing and using sensitive information like API keys in Google Cloud is to use Secret Manager. Secret Manager provides a secure and convenient way to store API keys, passwords, and other sensitive data. It allows you to reference secrets as environment variables in your Cloud Run application, which is both secure and easy to manage. Option A correctly describes this approach. Option B suggests mounting the secret key under a directory, which is not necessary and complicates the process without adding security benefits. Options C and D involve using Cloud KMS, which is more suited for encryption keys rather than storing API keys directly. Cloud KMS can be used to encrypt data, but for API keys, Secret Manager is the more straightforward and recommended solution.