The IUPAC name of the compound

$\displaystyle 3$-keto-$\displaystyle 2$-methylhex-$\displaystyle 4$-enal

$\displaystyle 5$-formylhex-$\displaystyle 2$-en-$\displaystyle 3$-one

$\displaystyle 5$-methyl-$\displaystyle 4$-oxohex-$\displaystyle 2$-en-$\displaystyle 5$-al

$\displaystyle 3$-keto-$\displaystyle 2$-methylhex-$\displaystyle 5$-enal