From the standpoint of reactivity, which is the poorest choice of dienophile to react with 2,3-dimethyl-1,3-butadiene in a Diels-Alder reaction?

From the standpoint of reactivity, which is the poorest choice of dienophile to react with 2,3-dimethyl-1,3-butadiene in a Diels-Alder reaction? #59 page 13 I think the answer is A, not B. Please advise. Thanks.https://docs.google.com/viewer?a=v&q=cache:uUPhrsZpKVgJ:www.usm.edu/phillipsgroup/CHE256_F2009/ch13_EC_answers.pdf+Which+of+the+following+dienes+would+you+expect+to+be+the+most+stable%3F+A)+CH3+CH2+CH%3DCHCH2+CH%3DCHCH3+B)+CH3+CH%3DCHCH%3DCHCH2+CH3+C)+CH2+%3DCHCH2+CH2+CH2CH%3DCH2+D)+CH2+%3DCHCH%3DCHCH2+CH2+CH3+E)+CH3+CH2+CH%3DC%3DCHCH2+CH3&hl=en&gl=us&pid=bl&srcid=ADGEESjSfrsfwJOS4jmIbE1r0Qhc0JZ8DUrWDpvLmsc9d0_mmoMOD0aLuIDHW44Onq4UMXtzBG-_-UTpcR9ioQ2t-QGZ3zcrPOm0th3MSyXlN9-r6XiDmKI-fYfPwfRAzvPkfUdJmMXY&sig=AHIEtbTN4f-6lW3foAvdZ0685O-P5sJj5A