Option D is the correct answer because ‘antagonist’ means ‘opponent
or enemy’. Thus, option D is the right option.
Option A is incorrect because ‘soldier’ means ‘person serving in army’. Thus, it
is not an appropriate meaning for the given sentence.
Option B is incorrect because ‘fighter’ means ‘a person fights’. Although ‘fighter’
is relatively similar in meaning it is not a completely appropriate meaning to
the given word.
Option C is incorrect because ‘protagonist’ means ‘the leading character’.
Thus, it is not a similar meaning to the given word.