Can someone explain why this question is an annuity due versus an ordinary annuity?

You have recently been hired as a consultant for a personal financial planning firm. One of your first projects is creating a retirement plan for a couple, Xavier and Elaine Cooper. They have just celebrated their 45th birthdays and after paying for their childrens education, they have decided to get serious about saving for retirement. Xavier and Elaine hope to retire 20 years from now (on their 65th birthdays), and they expect to live until age 90. Their hope is to be able to withdraw $125,000 a year from their retirement account the first withdrawal will occur on their 65th birthdays, and the 25th and final withdrawal will occur on their 89th birthdays. On their 90th birthdays, the account is expected to have a zero value (i.e., they dont expect to have any remaining funds left for their childrens inheritance). Xavier and Elaine currently have $300,000 saved in a retirement account, which consists of a portfolio of mutual funds that is expected to produce an annual return of 7%. To accomplish their goals, they would like to deposit an equal annual amount into their account starting one year from today (on their 46th birthdays) and continue to make those deposits through age 65. (Again, the account has an expected annual return of 7%.) Thus, they will make 20 annual end-of-year deposits to this account.