Answer:
exec
Step-by-step explanation:
The other three options (fork, waitpid, and pthread) are all primary functions for process control in various programming languages and operating systems.
fork: creates a new process by duplicating the calling process
waitpid: waits for a specific child process to terminate and returns information about its status
pthread: creates a new thread of execution within a process
However, exec is not a primary function for process control. While it is related to process control in that it is used to replace the current running process image with a new process image, it is not a fundamental or primary function for process control.