Which of the following commands allows an administrator to make a shell variable visible to subshells?

`export $VARIABLE` attempts to export the *value* of the variable as a new variable name, which is syntactically incorrect for exporting the variable itself.

The `export VARIABLE` command explicitly marks a shell variable named `VARIABLE` for export, making it an environment variable that will be visible and accessible to any subshells or child processes subsequently created from the current shell.

`set $VARIABLE` would attempt to set shell options or positional parameters based on the variable's value and does not make a variable visible to subshells.

`set VARIABLE` would either set shell options if `VARIABLE` is a valid option or treat `VARIABLE` as a positional parameter, neither of which exports the variable.

`env VARIABLE` would attempt to execute a command named `VARIABLE` within a new environment, or display the current environment, but it does not export a shell variable from the current shell.