Which of the following is one of the monomer of Buna-s?

$\begin{array}{1 1}(a)\;\text{styrene}&(b)\;\text{caprolactum}\\(c)\;\text{adipic acid}&(d)\;\text{isoprene}\end{array}$

1,3-Butadiene+Styrene$\quad \underrightarrow{\text{copolymerisation}}\quad$Buna-s
Hence (a) is the correct answer.