Answer: The Soviet Union shot down Korean Air Lines Flight 007 on September 1, 1983. The Soviet leaders believed that the aircraft was a U.S. spy plane conducting espionage activities in their airspace. Therefore, the correct answer is B. a U.S. spy plane. The incident resulted in the loss of 269 lives aboard the aircraft. It caused significant international controversy and heightened tensions between the United States and the Soviet Union during the Cold War era.