The folk song "Immigrant Song" in northern Shaanxi sings: "The mountains and rivers are beautiful, the world is flat, and Chairman Mao leads Shaanxi, Gansu and Ningxia. Welcome immigrants to open moun

The folk song "Immigrant Song" in northern Shaanxi sings: "The mountains and rivers are beautiful, the world is flat, and Chairman Mao leads Shaanxi, Gansu and Ningxia. Welcome immigrants to open mountains and forests. Our border areas are red everywhere. " folk song C

Test analysis: The information of "Shaanxi-Gansu-Ningxia Border Region" appeared in the materials. The Shaanxi-Gansu-Ningxia Border Region is the proper name of the northern Shaanxi base area where the Central Committee of China is located after the outbreak of the Japanese full-scale war of aggression against China and the second cooperation between the two countries. The combination option should appear in the background of cooperation among countries after the August 13th Incident in 1937, so C is chosen. A is 193 1 years ago, b is 1936 years ago and d is 1945 years later.