Concept:Stress is the emphasis placed on a particular syllable when pronouncing a word.Explanation:In "enlighten", the stress falls on the second syllable: en-LIGHT-en.In "unwanted", the stress falls on the second syllable: un-WANT-ed.In "agitate", the stress falls on the first syllable: AG-i-tate.In "Informal", the stress falls on the second syllable: in-FOR-mal.Only "agitate" has a different stress pattern from the rest.Answer:C. agitate