Working with a IoT application

Imagine an IoT application that has the source code as shown below for displaying files.

<?php

print(enter file name);

$file=_GET[‘filename’];

system(“cat $file”);

?>

Which of these inputs should be provided to this device to delete all files in the root directory?

Options

1. robot.txt
2. root rf
3. ‘a.txt; rm -rf /; ‘ “
4. a.txt’; ls /;