$3.$ Find out if the statement is true or false: In the classification of petroleum crudes, 'light' and 'heavy' refer to the oil's viscosity and boiling point range, with 'light' oils being easier to refine due to their lower sulfur content and higher yields of valuable products like gasoline and jet fuel.

$4.$ Find out if the statement is true or false: Thermal cracking is a modern petroleum refining technique that uses zeolite catalysts to break down heavier fractions into lighter, more valuable products such as ethylene and propylene, which are key feedstocks for the plastics industry.