Q. The term “Abyssal Plain” is related to which of the following?

[A] The plain which is formed due to glacial deposition.

[B] The plain which is formed due to river deposits.

[C] The underground plains are formed due water deposition and erosion.

[D] It is an underwater plain on the deep ocean floor.

Answer: D
Notes:

An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3,000 metres (9,800 ft) and 6,000 metres (20,000 ft).  

Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth’s surface. 

Source: NCERT – XI Fundamentals of Physical Geography