Which One of the Following Is True Regarding Structural Barriers

Which one of the following is true regarding structural barriers?

A) Structural barriers serve as psychological deterrents.
B) The objective of barriers is to cause as much delay as possible.
C) A series of barriers are usually used in any effective physical protection plan.
D) A series of concentric barriers should separate the area to be protected.
E) Even with good planning, most structural barriers do not prevent penetration by humans.
F) All of the above.