Final answer:
To select two files that are not adjacent, the Ctrl key should be used to click on each file individually.
Step-by-step explanation:
To select two files that do not appear next to each other, you would need to hold down the Ctrl key on the keyboard while clicking on each file individually. This action allows you to select multiple files that are not adjacent to each other in the file explorer or on the desktop. Holding down the Shift key, by contrast, allows you to select a consecutive group of files, while the Alt key and Spacebar do not serve the same purpose in file selection. This will allow you to select both files without any files in between being selected. The Ctrl key is commonly used for making non-consecutive selections in various computer applications.