(Brandenburger & Nalebuff). According to the arguments in this article, Delta Airlines and US Airways when they update their fleets because would be a. complementors; airplane manufacturers need enough airlines to buy their planes in order to recoup their cost of designing new airplanes. O b. complementors; providing better air traffic services is complementary to manufacturing new airplane designs. O c. c competitors; they compete for getting their orders for new airplanes filled first and getting more favorable conditions, which may provide them with a competitive advantage. d. substitutors; airplane manufacturers can at any time substitute the airlines as customers for their newly designed airplanes. e. substitutors; the airlines updating their fleets can more effectively substitute their air traffic services for those of the other airlines.