The diene shown reacts with acrylonitrile, $\mathrm{CH}{}_2=\mathrm{CH}-\mathrm{CN}$, by a Diels-Alder reaction. Which structure is the product?

The compound shown is buta-1,3-diene. The [4+2] cycloaddition forms two new sigma bonds between the diene termini and the two dienophile carbons, and the new double bond appears between the former C2 and C3 of the diene. The nitrile is therefore on a ring carbon two atoms from the double bond, giving cyclohex-3-ene-1-carbonitrile. The other structures have the double bond in the wrong place or are saturated.