As a member of O'Brien Corp's insurance committee discussing the types of underwriting principles that are followed by group insurance underwriting firms, which criteria are held to be true?

a. Require associates to deliver premium payments directly to the insurer.

b. The insured class average age should ideally move upward over time.

c. Obtaining insurance for the group should be tied to a specific goal.

d. A flow of people through the group is desirable.