Which of the following must be specified when launching a new Amazon Elastic Compute Cloud (Amazon EC2) Windows instance?

When launching a new Amazon Elastic Compute Cloud (EC2) Windows instance, specifying the Amazon EC2 instance type and the Amazon Machine Image (AMI) is essential. The Amazon Machine Image is crucial as it contains the operating system, including the specific Windows version you'd like to run, along with pre-installed software or configurations you may require. This selection defines the software environment of your instance.

Additionally, choosing the instance type determines the resources allocated to your instance, such as CPU and memory, which are critical for tailoring the performance of the application or service you plan to run. Each instance type is suited for different usage scenarios, and selecting the correct one impacts both the performance and cost of usage. Thus, these two factors are fundamental to the setup of any EC2 instance.