Explanation:

The relationship between 'haphazard' and 'methodical' is one of antonyms (opposites). Haphazard means lacking any obvious principle of organization, while methodical means done according to a systematic or established procedure. Similarly, 'arduous' means involving or requiring strenuous effort; difficult and tiring. Its antonym is 'facile', which means easily achieved or effortless. Options A (gruelling), B (hellacious), and C (strenuous) are synonyms of 'arduous', not antonyms.