Answer:
A. A change in the price of good X.
Explanation:
A demand curve plots price against quantity demanded. A change in price causes a movement along the demand curve according to the law of demand which says an increase in price leads to a reduction in quantity demanded and a fall in price leads to a rise in quantity demanded.
If the price of a complementary good increases, the demand for good x would fall and the demand curve would shift leftwards.
If income increases, and good x is a normal good, the demand curve would shift to the right.
If a change in taste and preference is in favour for good x, more of good x would be demanded and the demand curve would shift to the right.
I hope my answer helps.
