Which of the Following Is Not a Key Use Case

Which of the following is not a key use case for Windows Azure cloud computing:

A) Mobile apps-Use Windows Azure to support your mobile apps across a variety of platforms (e.g. ,Windows Phone 8,iOS,Android) -for example,authenticating app users,storing data and sending push notifications to users' devices.
B) Infrastructure-Set up servers in the cloud and scale your infrastructure (e.g. ,processor cycles,memory and secondary storage) as needed,paying for only what you use rather than purchasing additional costly hardware.
C) Storage,Backup and Recovery-Use Windows Azure's secure,reliable storage space to back up your data.The data is stored on servers in multiple locations worldwide to ensure that it's safe and accessible even in the case of a local disaster.
D) All are key use cases for Windows Azure.