Austro Hungary has the intention to build an international railroad, but it would only pass through Serbia, not through Bosnia, and connect Europe with Istanbull and continue to the Middle East. Some theorists claim that this was the main reason for the Austrian desire to dominate Serbia. That is why, in the ultimatum set to Serbia, Austria, among many points, also demanded full control of domestic affairs in the country. This request was the only one that was rejected by Serbia, and was formally the reason for the declaration of the war. On the other hand, dissatisfaction has been growing in Bosnia over the years since the Austrian annexation.
The answer is A.