Final answer:
An increase in utility (u) will result in a movement along the demand curve rather than a shift. Therefore, the correct answer is D. movement along the WS and PS curves.
Step-by-step explanation:
An increase in u refers to an increase in utility, which is a measure of satisfaction or happiness that a person derives from consuming a good or service. If u increases, it means that the person is becoming more satisfied or happier with the quantity of the good or service they are consuming.
This increase in u will result in a movement along the demand curve rather than a shift in the demand curve. This is because the change in u is caused by a change in the quantity demanded of the good or service, rather than a change in any other factors that would shift the entire demand curve.
So the correct answer is D. movement along the WS and PS curves.