Step 1: Background.
Belgium is known for its linguistic diversity, with Dutch, French, and German-speaking communities. This caused social and political divisions in the country.
Step 2: Analyzing the options.
(A) Belgium: Correct — social division was clearly based on language here.
(B) Northern Ireland: Divisions were mainly based on religion (Protestants vs Catholics).
(C) Bolivia: Divisions were mostly ethnic and class-based, not linguistic.
(D) Nepal: Divisions were mainly political and ethnic, not purely linguistic.
Step 3: Conclusion.
The correct answer is Belgium, where language was the basis of social division.