Which is the last line of defense in a physical security sense?
a. people
b. interior barriers
c. exterior barriers
d. perimeter barriers

(A) People

Explanation:

 The physical security system is the basically used in the information system. It is used in the technical and the administrator element in the security system. This is the technology oriented system that is basically used to prevent from the hacking attacks in the system.

So, the people is the last statement of the defense in the physical security as the various security system is basically used by various people.