Comprehensive Detailed Explanation:

The three primary and sequential functions of a Physical Protection System (PPS) are:

Detection – identifying unauthorized activity.

Delay – slowing intruder progress.

Response – intervening before asset compromise.

This layered approach ensures an opportunity to detect and intercept threats before they succeed.

A and D include " deterrence " or " prevention, " which are security goals but not primary PPS functions.

C lists valid concepts but omits the critical detection phase.