What is the main characteristic of the 1-2-1 defense in basketball?

I- One player is very advanced, two are at the limit of the zone, and two are close to the basket.
II- It focuses on defending players who play outside the three-second zone.
III- It aims to enhance defensive rebounding and defense of attackers who play near the basket.
IV- It is a system of play with more pressure and aggressiveness.
a) I and II are correct.
b) II and III are correct.
c) III and IV are correct.
d) I and IV are correct.