Concept:Plastics are formed by the polymerisation of small unsaturated molecules called monomers.Explanation:Ethene, C2H4, is an alkene used as a monomer.It undergoes addition polymerisation to form polyethene, a common plastic.Methane, calcium, and hydrogen are not used directly as monomers for making plastics.Thus, among the options, ethene is the raw material for the plastic industry.Answer:A. Ethene