You're designing a system to store large volumes of unstructured data where cost-efficiency, durability, and high availability are primary concerns. The solution must also support different storage classes for archiving. Which GCP service should you recommend?

*Explanation:* The most suitable choice is C. Cloud Storage with Object Lifecycle Management. It meets the requirements of cost-efficiency, durability, high availability, and supports different storage classes for archiving unstructured data. Options A, B, D, and E are not designed for this specific use case and do not provide the same level of flexibility and scalability as Cloud Storage with Object Lifecycle Management.