An annuity is a a. stream of payments (usually of decreasing size) made t equal time intervals for perpetuity O b. stream of payments (usually of increasing size) made at equal time intervals for a fixed period of time O c. stream of payments (usually of equal size) made at equal time intervals for perpetuity d. stream of payments (usually of equal size) made at equal time intervals for a fixed period of time O e. stream of payments (usually of decreasing size) made at equal time intervals for a fixed period of time C