An economist for a bicycle company predicts that, other things equal, a rise in consumer incomes will increase the demand for bicycles. This prediction assumes that:______.
a. there are many goods that are substitutes for bicycles.
b. there are many goods that are complementary to bicycles.
c. there are few goods that are substitutes for bicycles.
d. bicycles are normal goods.

He assumes that bicycles are normal goods. In Economics, a normal good is one which has an increase in demand when there is an increase in the income of the consumer. Hence, we can say that it has an income elasticity of demand that is positive.

Thus, we can say that normal goods are category of goods having a positive income elasticity of demand. The income elasticity of demand can be defined as the degree of responsiveness of demand to a change in the income of consumer. Hence, the income elasticity of demand for bicycle is positive as a result of the fact that its demand increases when there was an increase in the income of consumer