Which shell command is used to continue background execution of a suspended command?

The '&' operator is appended to a command at launch time to start it in the background initially; it cannot be used to resume an already-suspended job.

The 'bg' built-in sends SIGCONT to a suspended job (typically stopped with Ctrl+Z) and places it in the background, returning the shell prompt while the job continues executing.

'cont' is not a standard shell built-in or POSIX-defined command; sending SIGCONT to a process requires 'kill -CONT' or the 'bg' built-in.

'exec' replaces the current shell process with a new program and is entirely unrelated to job control or resuming suspended processes.

':&' is not recognized shell syntax for job control; the colon ':' is the null command and this combination does not resume suspended jobs.