The correct answer is grep -c 'refused' /var/log/auth.log because the -c option in the grep command provides a count of matching lines that contain the pattern specified. In this scenario, it counts the number of lines that have the word 'refused', giving an indication of the number of failed SSH login attempts logged in the 'auth.log' file. The options that include piping with the wc -l command are incorrect because when used with grep's -c option, they are redundant and unnecessarily complicate the command. The option that includes -v is incorrect because this inverts the match and would count all lines that do not contain the word 'refused'.