There are two categories of cash flows: single cash flows, referred to as "lump sums," and annuities. Based on your understanding of annuities, answer the following questions. Which of the following statements about annuities are true? Check all that apply. An ordinary annuity of equal time earns less interest than an annuity due. When equal payments are made at the beginning of each period for a certain time period, they are treated as ordinary annuities. Annuities are structured to provide fixed payments for a specified period of time. When equal payments are made at the beginning of each period for a certain time period, they are treated as an annuity due.