The correct answers are A and C. Amazon EC2 Auto Scaling (Option A) can improve the availability of a web application by automatically adjusting the number of EC2 instances in response to demand, ensuring that the application can handle changes in traffic without manual intervention. This helps in maintaining the performance and availability of the application even during peak times. Resources distributed across multiple Availability Zones (Option C) provide fault tolerance by ensuring that the application's components are not all located in a single data center. If one Availability Zone experiences an outage, the others can continue to operate, thus reducing the impact of failures on the application. Options B, D, and E, while useful in other contexts, do not directly address the improvement of availability and reduction of failure impact in the way that Auto Scaling and multi-AZ deployment do.