Scheduling three patients at 9 a.m. and three at 10 a.m. is...

Open scheduling, also known as "walk-in" scheduling, does not assign specific appointment times but rather allows patients to come in at their convenience. This method does not apply here, as the question specifies fixed appointment times for multiple patients, rather than an open-ended arrangement.

Cluster scheduling organizes appointments by grouping patients with similar needs or conditions together, but it typically involves scheduling them at different times rather than multiple patients simultaneously. Therefore, this option is not applicable as the scenario describes overlapping appointments rather than grouping by condition.

Double-booking refers to scheduling two patients for the same time slot, which can lead to conflicts and longer wait times if not managed properly. However, the wave scheduling method described allows for a structured approach to accommodate multiple patients effectively, distinguishing it from the chaos often associated with double-booking.