Wanda manages an application that fluctuates in usage quite a bit. Sometimes it uses quite a few servers with lots of memory and CPU while other times it only uses a couple of servers with minimal CPU and memory allocated to them. She doesn't have to manually make changes as the system has the ability to increase or decrease those resources on its own. Which of the following terms describes that capability?

a$.$ Scalability

b$.$ Elasticity

c$.$ Availability

d$.$ Reliability