A、unknown reasons. B、a training flight. C、the training formation. D、four bombs. A考查抓关键细节的能力。虽然其他三个选择项都与飞机消失有关，但真正的原因还未找出。

The United States Defense Department says genetic testing has identified the human remains found in the wreckage of a US Air Force jet that was missing on a training flight nearly a month ago. A Defense Department statement said the remains are identified as belonging to the pilot flying the A-10 jet which left the training formation and disappeared in circumstances which have still not been established. The wreckage of the aircraft which was armed with bombs was found last week in Snell in the Rocky Mountains in Colorado.