Final answer:
The '-v' option (a) is used with the compress command to display the compression ratio and detailed information about the files being compressed.
Step-by-step explanation:
When using the compress command to archive a set of files into a single file, the option to display the compression ratio of the individual files making up the new compressed file is -v, which stands for 'verbose'.
This option provides detailed information about the compression process, including the original size, compressed size, and the compression ratio for each file. The correct option from the provided choices would be a. ‘-v’.