Since we're talking about IaaS we can promptly discard D, array controller-based, since this is encryption at hw level, and in most cases is not an option for cloud providers.
Storage-based encryption involves encrypting data at rest, such as data stored on hard drives or in cloud storage. This is typically done using encryption keys that are managed by the cloud provider or by the customer. This method of encryption provides a high level of security, as it protects data from unauthorized access even if an attacker gains physical access to the storage media.
Instance-based encryption involves encrypting data in transit, such as data transmitted over a network or the internet. While this method can provide some level of security, it is not as secure as storage-based encryption, as it does not protect data when it is at rest.
Proxy-based encryption involves using a proxy server to encrypt data in transit. This method is similar to instance-based encryption, but it uses an additional layer of security by routing data through a secure server. However, it is still not as secure as storage-based encryption.