Question

services allow you to control costs effectively because you only pay for them when you are using them.
a o iaas
b o saas
c o paas

Explanation:

IaaS (Infrastructure - as - a - Service) allows users to pay for the infrastructure (like servers, storage) only when they are using it. SaaS (Software - as - a - Service) is software on - demand but the cost structure may not be as granular in terms of pure usage - based for infrastructure - like aspects. PaaS (Platform - as - a - Service) is more about providing a platform for development and deployment, and its cost model is not primarily centered around the same kind of infrastructure - usage - based cost control as IaaS.

Answer:

A. IaaS