Which one of the following is a correct definition?

1. A perpetuity is an infinite stream of equal payments which occur at the end of each time period.

2. An ordinary annuity is an infinite stream of equal payments which occur at the end of each time period.

3. A perpetuity is an infinite stream of unequal payments which occur at the end of each time period.

4. An ordinary annuity is a finite stream of equal payments which occur at the beginning of each time period.