Final answer:
In terminal operations, Ctrl + Z is used to suspend processes, not resume. To resume a suspended process in the background, use the bg command, and use fg to bring it to the foreground.
Step-by-step explanation:
The keyboard shortcut to resume terminal operations after they have been suspended is Ctrl + Z. However, this shortcut actually suspends the current foreground process. To resume a suspended process in the background, you use the bg command, and to bring it to the foreground, you use the fg command. To clarify the other options, Ctrl + C is used to terminate the current foreground process, Ctrl + D is used to send an EOF (End-of-File) to terminate an input stream, and Ctrl + R is used to search history backwards.