A technician is installing an operating system on a new computer.

The first step in installing an operating system on a new computer is Setting the boot order (Option A). This ensures that the computer can boot from the installation media (USB, DVD, etc.). Once the boot order is configured, the system can start from the installation source, and the rest of the OS installation process can proceed.

Formatting the hard drive (Option B) comes later in the process, after the installation media is booted.

Entering the product key (Option C) and Selecting the filesystem (Option D) are subsequent steps during the installation process.

CompTIA A+ Core 2 References:

1.9 - Perform OS installations and upgrades, including setting boot methods and boot order​​.