Whether usage

[karthikpandian19]

A little under a million years ago, the briny waters of the Baltic Sea began flooding into the cold North Atlantic: geologists are still debating whether the flood was gradual or created a cataclysm.
(A) whether the flood was gradual or created a cataclysm
(B) if the flood was gradual or created a cataclysm
(C) about whether the flood was gradual or cataclysmic
(D) whether the flood was gradual or cataclysmic
(E) whether the flood was gradual or it created a cataclysm

[shwetaprasad]

Answer: D

Reason: Whether is the correct usage here, if is more on the lines of probability.
Also, when we are using adjectives, the form they should be used in should be parallel, i.e., gradual and cataclysmic.

[Bill@VeritasPrep]

A little under a million years ago, the briny waters of the Baltic Sea began flooding into the cold North Atlantic: geologists are still debating whether the flood was gradual or created a cataclysm.

(A) whether the flood was gradual or created a cataclysm

(B) if the flood was gradual or created a cataclysm

(C) about whether the flood was gradual or cataclysmic

(D) whether the flood was gradual or cataclysmic

(E) whether the flood was gradual or it created a cataclysm

[GmatKiss]

IMO: D as well

[jordan23]

IMO D

A little under a million years ago, the briny waters of the Baltic Sea began flooding into the cold North Atlantic: geologists are still debating whether the flood was gradual or created a cataclysm.
(A) whether the flood was gradual or created a cataclysm
(B) if the flood was gradual or created a cataclysm
(C) about whether the flood was gradual or cataclysmic
(D) whether the flood was gradual or cataclysmic
(E) whether the flood was gradual or it created a cataclysm

[karthikpandian19]

OA is D,

Can you provide elaborate explanation on each option

A little under a million years ago, the briny waters of the Baltic Sea began flooding into the cold North Atlantic: geologists are still debating whether the flood was gradual or created a cataclysm.

(A) whether the flood was gradual or created a cataclysm

(B) if the flood was gradual or created a cataclysm

(C) about whether the flood was gradual or cataclysmic

(D) whether the flood was gradual or cataclysmic

(E) whether the flood was gradual or it created a cataclysm