a. The main(parent) chain should be the longest carbon chain feasible, including all carbons containing functional groups. With both functional groups in the main chain, the aforementioned option is the only one conceivable.

b. Because carboxylic and alcohol acids take precedence, the numbering begins with carboxylic carbon.

c. At the second carbon, there occurs a branching alkyl group substitution.

d. Because the 4th carbon has a hydroxyl group, it is known as 2-(2-methyl butyl)-4-hydroxybutanoic acid.