Concept:Cracking is the breakdown of large hydrocarbon molecules into smaller, more useful molecules using heat and a catalyst.Explanation:Large hydrocarbon molecules have long carbon chains.When they are heated at a high temperature in the presence of a catalyst, their bonds break.This produces smaller hydrocarbon molecules, such as alkenes.This process is called cracking.Cracking is important because it converts less useful heavy fractions into more valuable fuels and feedstock.Answer:C. cracking.