The correct structure to be named is based on IUPAC norms.

a. The main(parent) chain should be the longest possible carbon chain with all the carbons with the functional groups included in them. The above selection is the only possible one with both the functional groups in main chain.

b. Out of carboxylic acid and alcohol acid gets the priority hence the numbering starts from carboxylic carbon.

c. There is a branched alkyl group substitution at second carbon

d. There is a hydroxyl group at 4^th carbon therefore it can be named as 2-(2-methyl butyl)-4-hydroxybutanoic acid.