You wish to kill a process with a PID of 123. Select the command which will allow the process to “clean up” before exiting.

A.
kill -1 123

B.
kill -9 123

C.
kill -15 123

D.
kill -17 123

Explanation:
To tell a process to quit “at the earliest convinience” use the signal SIGTERM (15). If the process captures signals it can then either ignore it or “clean up” and terminate itself