Final answer:
The term 'open' indicates that patients are willing to change the date and time of their appointments as it signifies scheduling flexibility. Other options such as 'ASAP', 'fixed', and 'wait/will call' have different connotations regarding appointment scheduling preferences.
Step-by-step explanation:
The question asks which option indicates that patients are willing to change the date and time of their appointments. The correct answer is 'a. open'. When a patient's appointment preference is marked as 'open', it generally means that the patient is flexible with their scheduling and is willing to consider different dates and times for the appointment. On the other hand, 'ASAP' implies that the patient wants the earliest available slot, 'fixed' indicates an unwillingness to change the set appointment, and 'wait/will call' indicates that the patient will wait for a better time or will call back to reschedule.