The correct answer is B. Vendor lock-in. Vendor lock-in is a situation where a customer becomes dependent on a certain cloud provider and cannot easily switch to another provider without significant costs or disruptions. This can happen when the customer uses features or services that are only available from that specific provider, or when the customer has a large amount of data stored with the provider that is difficult to migrate. According to the web search results, vendor lock-in is a common concern in cloud computing1234. A service level agreement, a memorandum of understanding, and encrypted data are not barriers to switching providers, as they do not create a dependency on a specific provider or make it difficult to move data. For more information on vendor lock-in and how to avoid it, you can refer to the Cloudflare website1 or the Seagate blog4.