RE: Which of the below doesn't come under Performance ...
Answer is "C"
Both A and B come under Performance Testing.
You measure Server "Response time" to ensure that there are no Memory Leaks Bugs/Errors etc in the application.
Scalability also comes under Performance Testing and is interrelated with Response time. Its your job to test the application at hand to see if it is able to handle increasing amount of load in the manner it is supposed to.