$17.$ True or False: Polymerization is a refining process used to increase the viscosity of petroleum products.

$18.$ True or False: Hydrotreating is a refining process used to remove nitrogen impurities from crude oil.

$19.$ True or False: Catalytic reforming is a process used to convert low$-$octane gasoline components into high$-$octane ones.

$20.$ True or False: Butane is a common feedstock for the production of propylene.