Which diene and dienophile would react to give the following product?
A) Diene: 1,3-butadiene; Dienophile: Ethene
B) Diene: Ethene; Dienophile: 1,3-butadiene
C) Diene: Ethene; Dienophile: Ethene
D) Diene: 1,3-butadiene; Dienophile: 1,3-butadiene