male monkdeer

Whenever you're asked to support/strengthen a conclusion, you must first identify the logical gap.

Premise:
it is unusual for one non-carnivorous animal to fight another to the death.

Conclusion:
Vicious fighting is a cultural, rather than a genetic trait.

Logical Gap:
What supports the idea that it's cultural rather than genetic? Is there evidence that they learn from one another? Do different herds behave differently?

A. Monkdeer also have some unusual feeding habits that seem correlated with their location.
The fact that feeding habits are localized does not necessarily support the idea that fighting is a learned behavior.

B. Male monkdeer taken from the herd during infancy and raised by whitetail deer do not display the same aggression as male monkdeer raised by their own herd.
If this is true, then fighting is not an innate behavior - it's not genetic. This supports the idea that it's probably cultural instead. CORRECT

C. One large herd of jackelope found in the state of West Dakota seems to display aggressions similar to those of male monkdeer.
Evidence about another species is not relevant to an explanation about monkdeer.

D. Monkdeer are native to the state of West Dakota, and are rarely found far from that region.
Where they are found is not relevant to how they acquire fighting behavior.

E. Scientists have established that some monkdeer have culturally, rather than genetically, acquired traits in regard to the gathering of food.
Much like A, the fact that other habits are acquired culturally does not necessarily mean that fighting is acquired culturally.

The answer is B.