Teacher: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].
Teacher: Now, understand the problem? Solve this instance: (CNN) Syria's nascent ceasefire hung in the balance Monday after an airstrike on a United Nations aid convoy led the US to question Russia's commitment to calming violence in the war-torn country and its ability to influence its ally in Damascus. "What happened today has dealt a serious blow to efforts to bring peace to Syria," said a senior US administration official, who added that the strike "raises very serious questions about whether the Russians can deliver their end of the arrangement" to rein in the Syrian regime. Outrage after aid convoy, warehouse attacked in Syria Asked if the US was still open to extending ceasefire efforts, a second administration official said Russia now bears the burden of demonstrating its commitment to peace efforts, "otherwise, there will be nothing to extend and nothing to salvage."A ceasefire brokered by Russia and US enters its seventh day in SyriaCoalition strikes on Syrian troops caused a diplomatic row over the weekend 
 Question:At the same time, both the US and _ are in the skies striking terror targets.
Student:
Russia