Which of the following statement is correct?

a. An annuity due is best defined as a series of unequal payments occurring at unequal intervals for an unspecified number of periods at the beginning of each period.

b. Future cash outflows are less burdensome than present cash outflows of the same amount.

c. When the periodic payments are made at reqular intervals, we say that the cash flow streams are uneven.

d. A perpetuity is an annuity with a finite number of payments.

e. All the answers are incorrect.