$1.$ Which of the following is NOT a common refinery feedstock?

a$)$ Crude oil

b$)$ Natural gas

c$)$ Coal

d$)$ Biomass

$2.$ What is the primary purpose of a refinery feedstock?

a$)$ To produce electricity

b$)$ To generate heat

c$)$ To produce various petroleum products

d$)$ To serve as a lubricant

$3.$ Which of the following impurities is commonly found in refinery feedstock and can negatively impact refinery operations?

a$)$ Sulfur

b$)$ Oxygen

c$)$ Nitrogen

d$)$ All of the above

$4.$ What is the effect of sulfur impurities in refinery feedstock?

a$)$ Decreases corrosion in equipment

b$)$ Increases the octane rating of gasoline

c$)$ Leads to the formation of harmful emissions

d$)$ Improves the efficiency of refining processes