Answer:
D. a change in consumer income
Explanation:
There are two main reason for shift in demand curve left or right in addition to price:
Consumer income or earning affect the demand curve as according income of consumer, thier preference and priority changes. Example: Daily wages labor may have very less demand for Domino´s Pizza or starbucks coffee, however, manager of any MNC may have higher demand for Domino´s Pizza or starbuck coffee.