Which of the following types of activities between businesses would be considered illegal in the United States? Select all that apply. 

a. Delta, United, Southwest, and American airlines agree to restrict the number of flights they offer each day domestically in the United States. 

b. Archer Daniels Midland and the Japanese firm Ajinomoto agree to raise the price on lysine, an additive used in livestock feed. 

c. The cable television providers Comcast and Charter Communications agree not to compete in certain geographic regions of the country. 

d. Delta Airlines and Coke sign a contract to make Coke the exclusive provider of soft drinks on Delta flights.