Final answer:
Broad network access is an essential characteristic of the cloud model. Asynchronous communication, third normal form, and address mapping are not essential characteristics.
Step-by-step explanation:
A. Broad network access is an essential characteristic of the cloud model. This means that cloud services can be accessed over a network, allowing users to utilize the cloud from different devices and locations.
Asynchronous communication (B) refers to communication that doesn't require both parties to be present or active at the same time, which is not a characteristic of the cloud model.
Third normal form (C) is a concept in database design, not specific to the cloud model.
Address mapping (D) is not an essential characteristic of the cloud model.