Cloud computing is an abstraction based on the notion of pooling physical…

Cloud computing rests on virtualization: an abstraction layer that takes physical hardware resources (servers, storage, network capacity) drawn from a shared pool and represents them as logical, on-demand units decoupled from any single underlying machine. This software-defined resource behaves like a genuine one to the user but does not map one-to-one to a specific piece of hardware — this abstracted unit is what the industry calls a "virtual" resource.

In the given statement, cloud computing pools physical resources and presents them to the user as a single resource. Since what is presented is an abstraction of the underlying hardware rather than the hardware itself, the blank is completed by "virtual": "Cloud computing is an abstraction based on the notion of pooling physical resources and presenting them as a virtual resource." This is the standard, textbook definition of cloud computing.

Checking the remaining options against this definition:

• "real" describes the physical hardware itself — but the statement is specifically about how pooled hardware is represented to the user after abstraction, not the underlying devices, so this term misses the point of pooling altogether.

• "cloud" would make the definition circular — the sentence is defining "cloud computing", so using "cloud" to complete its own definition explains nothing.

• "none of the mentioned" is incorrect because one of the listed terms precisely names the property that pooled, abstracted hardware takes on in standard cloud-computing definitions.

Hence the completion that correctly matches the definition of cloud computing is confirmed.