The correct answer is A. High availability in AWS is achieved by ensuring that the application components are not only redundant but also distributed across multiple Availability Zones. This way, if one Availability Zone experiences an outage, the other zones can continue to operate, thus maintaining the availability of the application. Option A is the best practice as it places independent copies of the application in two or more Availability Zones, which is a standard approach to achieve high availability. Options B, C, and D do not provide the same level of redundancy and fault tolerance as A, which is why they are not the correct answers.