Knowing a patient's medical and dental history might affect

the drugs prescribed.
the length of the scheduled appointments.
the treatment plan.
all of the above.

all of the above.

Rationale: all of the above. Knowing a patient's medical and dental history is directly related to the treatment plan you are going to implement, the medications you may prescribe, and the length of the dental appointment. Some patients cannot tolerate certain medications, lengthy appointments where they are required to sit in one position for a long time, or if they are willing to even accept the treatment plan you are offering.