Draw the condensed structural formula and give the IUPAC name for each of the following:
a. A carboxylic acid that has the formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2},$ with no substituents
b. A carboxylic acid that has the formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2},$ with two methyl substituents