What are the elements of a systems approach to developing a physical protection system (PPS)?

What are the elements of a systems approach to developing a physical protection system (PPS)?
A . Assessment of needs Implementation of countermeasures Evaluation of effectiveness
B. Assessment of vulnerability Implementation of countermeasures Evaluation of effectiveness
C. Assessment of vulnerability Evaluation of effectiveness and Defence in Depth
D. Assessment of needs Implementation of countermeasures Evaluation of effectiveness

Answer: B