Definition: You are given a question on high school geography. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: Which of the following situations does NOT occur in a federal state?
(A)Central government possesses a two-level system of government. (B)Central government governs country as a single unit. (C)It often possesses a written constitution. (D)Lower-level divisions have unique powers.

B