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Contrite means to be regret one's action. Obdurate means to refuse to change one's views. The 2 words are antonyms.
Let us evaluate the options.
Option A:
Grievous means to do something bad and severe.
Lamentable is a term used to denote that the action is bad or deplorable.
The 2 words are synonymous.
Option C:
Sophisticated is a term used to describe a high degree of development.
Cultured and sophisticated cannot be termed antonyms.
Option D:
Assenting means to give the nod. Favourable and assenting cannot be termed opposite in meaning.
Option B:
Aphoristic is a term used to describe that the claim is a general truth or widely accepted.
Esoteric is a term used to denote something that is understood by a limited set of people.
The 2 terms are opposite in meaning and hence, option B is the right answer.