Which of the following would cause a shift in the demand curve loading from point a to point b?
a. an increase in income (normal good)
b. a decrease in income (inferior good)
c. an increase in the price of a substitute good
d. all of the above

The correct answer is D. All of the above.

Explanation:

Each good will have its characteristic demand curve, more or less inclined, more or less convex. In addition, the position of the curve, higher, lower, shifted to the left or right, will depend on several factors:

If the income of the consumers grows, the demand will be increasing, which will cause the shift to the right of the demand curve since at the same price the quantity demanded will be greater. On the contrary, if the country's income decreases, the demand will decrease and the demand curve will shift to the left.

Similarly, the curve will shift to the right if demand increases due to a positive change in tastes or fashion or because the prices of products that can replace it increase.

However, that the lowering of the product itself does not produce displacement of the curve since the curve is indicating precisely the quantities demanded at any price. If the aforementioned factors are constant, then the demand curve will not move and we can measure exactly the effect of price variations on the quantities demanded, which will be represented by movements along the curve