Factors that could cause a demand curve to shift to the left include all of the following except:

a.a change in preferences away from the product in question.

b.an increase in the price of substitute products.

c.a growing awareness of a health risk associated with the product.

d.a decrease in the general level of income in the country.

e.All of the factors listed above could cause a demand curve to shift to the left.

*Please explain.