Solution

Option (a) is the correct answer. ‘Cogent’ means ‘(of an argument or case) clear, logical, and convincing.’, hence, a cogent argument, reason, etc. is clearly expressed and persuades people to believe it. Here the synonym of cogent is ‘forceful’ which ‘means strong and assertive; vigorous and powerful.’ ‘Objectionable’ means arousing distaste or opposition; unpleasant or offensive. ‘Exceptional’ means not like most others of the same type; unusual ‘False’ means not according with truth or fact; incorrect.