Which solution meets these requirements?

Explanations:

Launching all EC2 instances in the same Availability Zone with a cluster placement group optimizes network throughput and minimizes data transfer charges. This setup allows for low-latency communication between instances, essential for a latency-sensitive application processing high transaction volumes.

Although launching EC2 instances in different Availability Zones can improve availability and fault tolerance, it increases data transfer costs due to cross-AZ data transfer charges. The partition placement strategy is not optimal for minimizing latency and maximizing throughput for in-memory databases.

While deploying an Auto Scaling group based on network utilization can help manage capacity, launching instances in different Availability Zones does not minimize data transfer charges. It can also lead to higher latencies due to inter-AZ traffic.

Deploying an Auto Scaling group with a step scaling policy to launch EC2 instances in different Availability Zones does not address the requirement for minimizing data transfer costs and latency. This option does not effectively optimize for the specified use case of high transaction throughput.