Detailed Instructions: In this task, you're given a statement, further information available on a particular linked term from the statement, and a question. Your job is to generate the answer to the question by using the information provided. If there is no clear answer obtainable, output 'none'.
Problem:Context: Following the occupation of Serbia by the Central Powers, Link Information: The Central Powers consisted of the German Empire and the Austro-Hungarian Empire at the beginning of the war. The Ottoman Empire joined the Central Powers later in 1914. In 1915, the Kingdom of Bulgaria joined the alliance. Question: How many nations were part of the powers that occupied Serbia?
Solution:
Answer: 4