Which Is an Example of a Change in Product Demand

Which is an example of a change in product demand that decreases labor demand?

A) An increase in the price of paper increases the cost of making books, thus decreasing the demand for bookbinders.
B) The widespread availability of self-serve gas pumps reduces the demand for workers pumping gas.
C) An increase in the price of steel increases the cost of producing cars and trucks, thus decreasing the demand for automobile workers.
D) A decline in productivity in retailing decreases the demand for retail sales workers.