$21.$ The process of breaking down large hydrocarbons into smaller ones by the action of heat and catalysts is called:

a$)$ Cracking

b$)$ Reforming

c$)$ Alkylation

d$)$ Polymerization

$22.$ Which of the following is not a method of petroleum transportation?

a$)$ Pipeline

b$)$ Tanker ships

c$)$ Rail

d$)$ Teleportation

$23.$ The refining process used to improve the color and odor of petroleum products is called:

a$)$ Cracking

b$)$ Reforming

c$)$ Alkylation

d$)$ Hydrotreating

$24.$ The process of converting low$-$octane hydrocarbons into high$-$octane components by combining them with isobutane is known as:

a$)$ Cracking

b$)$ Reforming