In the Case Study "Sun Country Versus Northwest Airlines," Sun

In the case study "Sun Country versus Northwest Airlines," Sun Country's error was:

A) Failing to use backward induction.
B) Ignoring Northwest's possible reaction to its decision begin regularly scheduled nonstop service to Boston, New York, Washington, D. C., Los Angeles, and seven other destinations.
C) Assuming that Northwest would continue to charge competitive prices.
D) Answers b and c are correct.
E) All of the above.