Answer: D. decrease in quantity demanded.
Step-by-step explanation:
A change in demand is caused by the factors that affect demand except the price. The movement along the demand curve is as a result of the price change.
An increase in demand will lead to the rightward shift of the demand curve and a decrease in send will lead to the leftward shift of the demand curve.
On the other hand, an increase or decrease in the quantity demanded will lead to the movement along a given demand curve.
Based on the question, when there is an increase in the price of carrying cases for wireless earbuds, this will lead to a reduction in the quantity demanded of wireless earbuds as less people will buy the earbuds.