Due to wider commercial availability of audio recordings of authors reading their own books, sales of printed books have dropped significantly. Which one of the following conforms most closely to the principle illustrated above? ['Because of the rising cost of farm labor, farmers began to make more extensive use of machines.', 'Because of the wide variety of new computer games on the market, sales of high-quality computer video screens have improved.', 'Because neither of the two leading word processing programs has all of the features consumers want, neither has been able to dominate the market.', 'Because a new brand of soft drink entered the market, consumers reduced their consumption of an established brand of soft drink.']