The IUPAC name for the following compound is:

$\displaystyle 2$, $\displaystyle 5$-dimethyl-$\displaystyle 6$-oxo-hex-$\displaystyle 3$-enoic acid

$\displaystyle 6$-formyl-$\displaystyle 2$-methyl-hex-$\displaystyle 3$-enoic acid

$\displaystyle 2$, $\displaystyle 5$-dimethyl-$\displaystyle 5$-carboxy-hex-$\displaystyle 3$-enal

$\displaystyle 2$, $\displaystyle 5$-dimethyl-$\displaystyle 6$-carboxy-hex-$\displaystyle 3$-enal