The correct option is D
Sodium borohydride is a mild reducing agent, it will reduces aldehyde and ketones to alcohols, but does not reduce esters, carboxylic acids or amides.
5-hydroxyhexanoic acid
Product A is 5- hydroxyhexanoicacid. It has both alcohol and carboxylic acid group in it. Thus, it undergoes intramolecular esterification in the presence of acid and forms the cyclic ester product.
\( \stackrel{ H ^{+}}{\longrightarrow} \)