Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: NATO's top military commander expressed concern Sunday about the buildup of Russian forces on Ukraine's border, as Moscow's forces consolidated their control of Crimea over the weekend. Supreme Allied Commander Europe Gen. Philip Breedlove said Russia had a large force on Ukraine's eastern border and that he was worried it could pose a threat to Moldova's separatist Trans-Dniester region. "The (Russian) force that is at the Ukrainian border now to the east is very, very sizable and very, very ready," Breedlove, a U.S. Air Force general, said. "There is absolutely sufficient force postured on the eastern border of Ukraine to run to Trans-Dniester if the decision was made to do that, and that is very worrisome."NATO commander says Russia has a large force on Ukraine's eastern border"Russia is acting much more like an adversary than a partner," NATO commander says"We must not allow a new division of Europe," says German foreign ministerPro-Russia rallies planned in southern, eastern Ukraine 
 Question:"It's deeply concerning to see the _ troop buildup along the border.

Russian