Xavier Is an Ethnographer Studying Doctor/patient Relations

Xavier is an ethnographer studying doctor/patient relations. As a certified Physician's Assistant, he agrees to donate some of his skills in the weekend clinic in return for the opportunity to conduct his study. While doing his work, he meets with patients and physicians and is able to play both the role of observer and physician's assistant.
-In this scenario, Xavier best represents which of the following types of observer?

A) Active participant observer
B) Privileged, active observer
C) Passive observer
D) Nonformal observer