This is a tricky question which tests your reading comprehension.
If a and b are integers (with a not zero), we say a divides b if there is an integer c such that b = ac.
From the stimulus, we know that n MUST have a factor of 12. So 12 is the largest positive integer that MUST divide n. This means that for all possible values of n, 12 is the largest positive factor that each value of n MUST have.