Answer:
A). Fault tolerance
Step-by-step explanation:
The Microsoft Azure is described as the cloud computing service that is known for its flexibility, cost-effectiveness, and quick and easy compliance to fulfill the company's requirements.
As per the question, in order to ensure that 'some servers are available in case of a single Azure data center going offline for an increased time period', the recommendation must include the 'fault tolerance' ability of Azure services. Azure infrastructure has the ability to immediately react in case of a failure to restore the servers and its services. In case of hardware failure, crashing of hard-disks, or short-term availability problems with servers, Azure predicts and manages such failures effectively. Thus, option A is the correct answer.