A short fragment of a copolymer chain (three repeat units, end groups shown) is drawn. The monomers are shown as pairs of molecules among the structures. Which pair of monomers gives this copolymer?

The chain contains C=C bonds (from a diene added 1,4) and a cyano-bearing carbon (from a vinyl monomer). This is Buna-N (nitrile rubber), a copolymer of buta-1,3-diene and acrylonitrile. A styrene pair would show a phenyl ring, an isoprene pair would show methyl branches on the double bonds, and acrylamide would give an amide, not a cyano, group.