4. Which of the following statements is (are) true for the Diels-Alder reaction?
(A) When the diene is electron-rich, the reaction works best when the dienophile contains one or moreelectron-withdrawing groups conjugated to its C=C.
(B) Substituents which are cis in the dienophile remain cis in the product.
(C) Dienes which cannot achieve an s-cis conformation do not react in Diels-Alder reactions.
(D) Secondary orbital interactions typically cause the endo product to be favored kinetically over the exo.
(E) All of the above.