To ensure Data Loss Prevention (DLP) efficiency and prevent the exposure of sensitive data in a cloud environment, the administrator should implement **Classification**.
Classification involves categorizing data based on its sensitivity and importance. This categorization allows for the enforcement of policies that dictate how different types of data should be handled, shared, or stored. With proper classification, sensitive data can be identified, and DLP policies can be configured to ensure its protection, including measures like encryption, access controls, and monitoring.
So, the correct answer is **C. Classification**.