Concept:In compound nouns like “head of state”, only the main noun takes the plural form.Explanation:The word “several” shows that more than one person is meant.So we need the plural form of “head of state”.In this compound phrase, “head” is the noun that becomes plural, while “state” stays singular.This gives the correct plural form: “heads of state”.Therefore, the correct option is the one that uses “heads of state”.Answer:C. heads of state