Which of the following is a benefit of AWS cloud computing that helps lower variable costs?

Economies of scale is the correct answer because AWS, by operating at a massive scale, can achieve lower costs per unit of compute, storage, and other services. These savings are then passed on to customers, reducing their variable costs compared to operating their own data centers. High availability, global reach, and agility are all significant benefits of AWS cloud computing, but they primarily relate to reliability, accessibility, and speed of deployment, respectively, rather than directly lowering variable costs through shared infrastructure efficiencies.