Which is the best synonym of ferocity from the options given below?

Choice A is correct because 'viciousness' signifies 'the quality of being savage, fierce' and pertains to the severity of the warriors; it is synonymous with 'ferocity.'

'Bravery' is a good trait that means 'to have bravery,' it's a heroic quality, but 'ferocity' does not indicate courage, it's not a heroic quality, and it has a negative connotation, so choice B is incorrect. As a positive characteristic, 'terrific' signifies anything extremely excellent or amazing; as a negative characteristic, it denotes 'having the power to cause fear or panic.' Despite having a similar connotation to 'ferocity,' the latter is archaic and hardly used nowadays.

Option C is incorrect because 'terrific' is often used to describe anything nice, however 'ferocity' does not describe anything or someone positive.