Which of the following best describes the structure of an annuity? A. a series of payments to be received during a period of time. B. a series of payments to be received at a common interval during a period of time. C. a series equal payments to be received at a common interval during a period of time. D. the present value of a set of payments to be received during a future period of time. Select one: a. D O b. A . O d. B