Which Is an Example of a Change in Productivity That

Which is an example of a change in productivity that increases labor demand?

A) Mail-order catalog sales rise, thus increasing the demand for workers in the mail-order business.
B) Sport utility vehicles increase in popularity, thus increasing the demand for the workers who make them.
C) A decrease in the price of lumber decreases the cost of building homes, thus increasing the demand for construction workers.
D) A technological change increases output per worker in the computer industry, thus increasing the demand for computer workers.