The correct answer is A. Isoprene.
Natural rubber is a polymer of isoprene, a five-carbon hydrocarbon. It is produced by the polymerization of isoprene monomers, which are linked together to form long chains. These chains are then twisted and folded into a three-dimensional network, which gives natural rubber its elasticity and strength.
Isoprene is a naturally occurring compound that is found in the sap of many plants. It is also produced synthetically.
Styrene is a six-carbon hydrocarbon that is used to make polystyrene, a type of plastic.
Butadiene is a four-carbon hydrocarbon that is used to make synthetic rubber.
Ethylene is a two-carbon hydrocarbon that is used to make polyethylene, a type of plastic.