$1.$ Which of the following is NOT a common type of 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 manufacture plastics

$3.$ Which of the following impurities in refinery feedstock can negatively impact the refining process?

A$)$ Sulfur

B$)$ Oxygen

C$)$ Nitrogen

D$)$ All of the above

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

A$)$ Increases the efficiency of refining

B$)$ Leads to corrosion of equipment

C$)$ Improves product quality

D$)$ Reduces environmental emissions