Weber's law implies that a postal clerk who judges by hand whether an envelope needs extra postage will be most accurate when judging a(n)

Weber’s law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. It does not hold for extremes stimulation. In the question, whether an envelope needs extra postage will be most accurate when judging a heavy envelope of 12 ounces.  

Ais the correct answer