The correct answer is D. Countries sometimes seek allies to preserve the balance of power.
Step-by-step explanation
The image shows a graph in form of balance that describes the alliances between countries during World War I. In the right part, is shown the main triangle of the Triple Alliance in which were Italy, Germany, and Austro-Hungary (Serbia), also in the below part is Romania who allied a year after (1883) to be in this coalition in 1882. On the left side are shown the countries involved in the Triple Entente, which were Great Britain, Russia, Japan, and France also at the bottom was the Balkan League that joined this collation in 1912 (several years after the formation of the alliance). This image shows that the alliances had a similar number of members to have a balance of power during the war. Also, the form of balance allows concluding that there was equality of forces between both factions. Therefore, the correct answer is D. Countries sometimes seek allies to preserve the balance of power.