I assume that you meant to show a problem and four possible answers -- but you didn't show the problem. Well, answer 2 is out because that is not a difference of logs, it is the sum of logs. Your problem must be the log to some base, hopefully it is either 4 or 8, of a fraction. If the base is 4, then the first answer is correct. If the base is 8 and the numerator of your fraction is 1, then the third answer is correct. If the base is 8 and the numerator is 2 (or if you don't have a fraction and the argument is just 2), the fourth answer is correct.