A company wants to start using Azure services. They have several departments that would need to make use of Azure services. They want to give each department the ability to use a different payment option for the amount of Azure services they consume. Which of the following should each department use to fulfill this requirement?

Answer options:

A.A resource group
B.A subscription
C.An Azure policy
D.A reservation

Answer – B 
The billing for Azure resources is tagged to a subscription. Hence to segregate the billing for each department, each of them can have a different subscription. 
For more information on subscriptions, please visit the below URL which refers to a blog article on the benefits of a Windows subscription- 

https://blogs.msdn.microsoft.com/arunrakwal/2012/04/09/create-windows-azure-subscription/