Step 1: Understanding the Concept:
This is a sentence completion question that tests vocabulary. The second part of the sentence, following the colon, defines or explains the word that should go in the blank.
Step 2: Detailed Explanation:
The clue in the sentence is "most of them knew very little about foreign countries." This description points to a word that means isolated, inward-looking, or having a narrow worldview. We need to find the vocabulary word that best matches this definition.
Analyzing the Options:
(A) partisan: Means a strong supporter of a party, cause, or person. This is unrelated to knowledge of foreign countries.
(B) erudite: Means having or showing great knowledge or learning. This is the opposite of knowing "very little."
(C) insular: Comes from the Latin word "insula," meaning island. It means ignorant of or uninterested in cultures, ideas, or peoples outside one's own experience. This perfectly describes people who know very little about foreign countries.
(D) cosmopolitan: Means familiar with and at ease in many different countries and cultures. This is the direct opposite of the clue.
(E) imperturbable: Means unable to be upset or excited; calm. This describes a temperament, not a level of worldly knowledge.
Step 3: Final Answer:
The word "insular" accurately describes a population that knows very little about the outside world, matching the clue given in the sentence.