Abyssal plains are very flat features that form

The correct answer is - the seafloor is spreading.

The abyssal plains are formed by the spreading of the seafloor that appears where the tectonic plates move away from one another. They are one of the flattest and smoothest surfaces on the planet. The abyssal plains are located between the mid-ocean ridges and the foot of the continental rise. Their depth in general is between 3,000 m and 6,000 m.

These features are actually occupying a staggering 50% of the Earth, and the fact that they are the least explored features of all, just makes us wonder and imagine what lies hidden down there.

answer; three;