The school's track and field day will pit even-numbered grades against odd-numbered grades. All the first-place ribbons for the even-numbered grades will be compared to the first-place ribbons for the odd-numbered grades to determine the winner. As a learning experience, the third graders are asked to sort out which grades are odd and which grades are even. Using the definition of even and odd numbers, how will the third graders determine which grades are odd or even?