Suppose a physics student is interested in exploring graduate school in the northeast. The student identifies a program of interest and finds the name of $6$ students from that program to interview. In this context, identify what is meant by the a$.$ subject, b$.$ sample, and c$.$ population.

a$.$ What is the subject in this context?

A$.$ all students enrolled at graduate schools in the northeast

B$.$ the graduate schools in which the physics student is interested

C$.$ the physics student conducting the interviews

D$.$ each student in the physics program