Sentence Correction

The characteristic phenomenon of mass suicide by thousands of lemmings year after year by jumping off from cliffs to great depths, explainable only by a chosen few behavioral scientists, occurs after a majority of the animals is driven to migrate from friendly habitats to hostile environs

(A) explainable only by a chosen few behavioral scientists, occurs after a majority of the animals is

(B) explainable by a choice few behavioral scientists, only occurs after a majority of the animals are

(C) explainable only by a choice few behavioral scientists, occurs after a majority of the animals are

(D) is explainable only by a choice few behavioral scientists, occurs after a majority of the animals are

(E) that can be explained only by a choice few behavioral scientists and it occurs after a majority of the animals are

C is by a choice few behavioral scientists correct in OA

(A) explainable only by a chosen few behavioral scientists, occurs after a majority of the animals is

(B) explainable by a choice few behavioral scientists, only occurs after a majority of the animals are

(C) explainable only by a choice few behavioral scientists, occurs after a majority of the animals are - correct

(D) is explainable only by a choice few behavioral scientists, occurs after a majority of the animals are

(E) that can be explained only by a choice few behavioral scientists and it occurs after a majority of the animals are - wordy

what is the source of this question? none of the option seems correct!!
"explainable only by a choice few behavioral scientists" seems wrong in option C

vipulgoyal wrote:The characteristic phenomenon of mass suicide by thousands of lemmings year after year by jumping off from cliffs to great depths, explainable only by a chosen few behavioral scientists, occurs after a majority of the animals is driven to migrate from friendly habitats to hostile environs

(A) explainable only by a chosen few behavioral scientists, occurs after a majority of the animals is

(B) explainable by a choice few behavioral scientists, only occurs after a majority of the animals are

(C) explainable only by a choice few behavioral scientists, occurs after a majority of the animals are

(D) is explainable only by a choice few behavioral scientists, occurs after a majority of the animals are

(E) that can be explained only by a choice few behavioral scientists and it occurs after a majority of the animals are

There is no correct answer here.
The OA includes the following errors:

suicide by thousands by jumping
Here, both modifiers (by thousands and by jumping) serve to modify the same preceding noun (suicide), but the two modifiers are not connected by a conjunction.
This construction is not viable.

Also, by + VERBIng typically serves as an ADVERB, indicating HOW an action is performed.
But here, by jumping serves as an ADJECTIVE modifying suicide -- a very awkward construction.

to great depths, explainable only by a choice few scientists
Here, explainable (adjective) seems to modify depths (the nearest preceding noun), implying that GREAT DEPTHS are explainable.
Not the intended meaning.

Ignore this SC.
What is the source?