Which of the Following Is Not Considered to Be a Level

Which of the following is not considered to be a level one collection reminder?

A) If your payment is not received in 10 days,your account will be referred to a collection agency.
B) Prompt payment for regular dental checkups is appreciated.
C) If there is any reason for not paying this balance,please contact us.Thank you.
D) Have you overlooked your balance due? You agreed to send a check after your recall appointment.