$67.$ The primary application of $\_\_\_,\_\_\_,$ and $\_\_\_\_\_$ in the petrochemical industry is the synthesis of various polymers, resins, and fibers used in manufacturing. $($a$)$ Polyethylene, polypropylene, polystyrene $($b$)$ Methanol, ethanol, butanol $($c$)$ Butadiene, acetylene, styrene $($d$)$ Ethylene, propylene, butylene

$68.$ The production of $\_\_\_\_,\_\_\_\_,$ and $\_\_\_\_\_\_$ involves the thermal or catalytic cracking of hydrocarbons to yield smaller, more valuable molecules. $($a$)$ Ethylene, propylene, butylene $($b$)$ Acetylene, synthesis gas, hydrogen $($c$)$ Naphthenes, aromatics, alkanes $($d$)$ Methanol, ethanol, propanol