Explanation

The minimum length of the mirror must be at least half the height of the person to see a full image. Option A is correct because it matches the required minimum length (half of 6 feet). Option B is incorrect because it is too long for the minimum requirement. Option C is incorrect because it is longer than the minimum required length but not necessarily the *minimum*. Option D is incorrect because it is less than half the height and will not show a full image.