D client can only authorise testing of systems and infrastructure it actually owns or controls; the underlying infrastructure of a shared cloud platform is owned and controlled by the cloud provider, not the client, so testing it without the cloud provider's own authorisation (many providers publish specific permitted testing policies and require notification or approval for certain activity) would not be properly authorised and could expose the tester to real legal risk, regardless of the client's consent. Cloud infrastructure is not "unowned" (A) - it has a clear legal owner/operator - and client consent, while necessary for testing the client's own configuration and data within the environment, is not sufficient on its own to authorise testing of the provider's underlying infrastructure (contradicting both D and C's extremes).