For Many Years, Southwest Airlines Distinguished Itself as the Low-Cost

For many years, Southwest Airlines distinguished itself as the low-cost airline. Now, many other low-cost competitors have entered the market. Similarly, Southwest was one of the first airlines to offer online ticketing. Now, all airlines have online ticketing. These examples suggest that

A) no single strategy is likely to be sufficient to build a sustainable competitive advantage.
B) a situation analysis does not accurately predict a firm's strengths.
C) customer excellence cannot be achieved.
D) product excellence is the only true source of a sustainable competitive advantage.
E) innovation is pointless because competitors will develop copycat offerings.