Final answer:
The blood pressure reading within the expected reference range for an adolescent patient is 110/70 mm Hg, consistent with standard reference ranges for blood pressure just below the normal adult range of 120/80 mm Hg.
Step-by-step explanation:
An EKG technician should recognize that the blood pressure reading within the expected reference range for an adolescent patient is 110/70 mm Hg. According to the guidelines from the American College of Cardiology and American Heart Association, normal blood pressure is less than 120/80 mm Hg, and readings above this range can indicate prehypertension or hypertension. For adolescents, blood pressure readings can be slightly lower than adults but are generally expected to be close to the adult range. Therefore, option b) 110/70 mm Hg is within the expected reference range for adolescents.