The correct option is A Most
The option A is correct because there's an error with the usage of the word 'most' because a superlative is not added before the word 'unique' as it means 'one of a kind' and if we add very it would be redundant. 'The' is used because in all cases the noun is specific and is known to the speaker and listener, hence it's not an error, option B is incorrect. 'It' is a pronoun which modifies the noun 'bridal gown'. Since there's no error in the option, option C is incorrect. Similarly, 'his' is a pronoun for 'bridegroom', there's hence option D is incorrect. There is an error in the sentence, hence E is incorrect.