Jenny bakes a cake for her sister's birthday party and asks the guests how the cake tastes. They tell her that the cake is too sweet. Jenny realizes that she must reduce the amount of sugar she adds to the cake by at least half a cup the next time so that the guests will notice it is less sweet than the previous one. Which of the following concepts does this example most closely illustrate?

A. mutationB. difference thresholdC. adaptationD. absolute threshold