Scandinavian Airlines System recently announced the purchase of 35 Boeing 737-600 airliners, with the option to buy another 35 for a total of $2.4 billion. SAS called Boeing "a professional and solid supplier." Deliveries began in late 1998 and will continue for some years to come. This arrangement between Boeing and SAS is an example of:
A) reciprocity.
B) exclusive dealing.
C) review marketing.
D) a long-term buyer-seller relationship.
E) a tying arrangement.
Answer: D