The answer is c: opening Finder and selecting the files.
Explanation for each option:
a. Searching for files with a .zip extension: This option is incorrect because Riley wants to create a compressed file, not search for existing ones.
b. Starting File Explorer and right-clicking the files: This option is incorrect because File Explorer is a feature of Windows, not Mac. Riley is using a Mac, so she should use Finder instead.
c. Opening Finder and selecting the files: This is the correct option. On a Mac, Finder is the file management application. Riley can select the files she wants to compress, right-click, and choose the option to compress them into a single .zip file.
d. Downloading compression codec software: This option is unnecessary because macOS has built-in functionality to compress files into a .zip format without needing additional software.
Summary:
Riley should open Finder and select the files she wants to compress. This will allow her to create a .zip file that she can easily email to her colleague.