$63.\_\_\_,\_\_\_,$ and $\_\_\_\_\_$ are primary petrochemical precursors used in the production of a wide range of synthetic materials, including plastics, fibers, and rubbers. $($a$)$ Ethylene, propylene, butylene $($b$)$ Hydrogen, synthesis gas, acetylene $($c$)$ Methane, propane, butane $($d$)$ Polyethylene, polypropylene, polyvinyl chloride