Final answer:
For running a questionnaire application for only one day without interruption, On-Demand Instances are the best choice as they offer hourly or secondly billing with no long-term commitments, ensuring the application runs uninterrupted for the required duration.
Step-by-step explanation:
If you want to run a questionnaire application for only one day without interruption, the most appropriate Amazon EC2 purchase option would be On-Demand Instances. On-Demand Instances allow you to pay for compute capacity by the hour or the second with no long-term commitment. This flexibility makes them ideal for short-term, irregular workloads that cannot be interrupted, exactly like running an application for a single day.
Reserved Instances are typically more cost-effective for applications that have a steady state or a predictable usage pattern, as they require a commitment for one to three years. Spot Instances allow you to bid on unused EC2 capacity and are best suited for workloads that have flexible start and end times. However, Spot Instances can be interrupted by EC2, which is not suitable for your circumstances. Dedicated Hosts are physical servers with EC2 instance capacity fully dedicated to your use and are generally used for licensing requirements that don't allow multi-tenant virtualization or for regulatory reasons, thus are unnecessary for running a questionnaire for a day.