Jason, a personal care product manufacturer, incorporates customers' suggestions in designing a new line of safety razors for men. The new product is launched with thinner, finer blades. However, when the new razors reach the market, customers fail to notice any improvement in them. In the given scenario, the customers' reactions indicate that the new razor design has failed to register the _____.
A. mere exposure effect
B. mere association effect
C. just meaningful difference
D. just noticeable difference