Which statement is an example of substitute goods affecting demand?

a. A bumper crop of cotton lowers the price of cotton clothing. Sales of silk shirts decrease.
b. As laptop computer sales increase, so do the sales of computer cases.
c. An automobile maker lays off thousands. Sales of electronic goods in that city fall.
d. Hi-tech companies lure people to a region. Demand for housing rises.

Answer: a. A bumper crop of cotton lowers the price of cotton clothing. Sales of silk shirts decrease.