题目内容：

In 1929, three years after his1. (fly） over the North Pole, the American explorer, R.E. Byrd, successfully flew over the South Pole for the 2.（one） time. Though, at first, Byrd and his men were able to take a great many photographs of the mountains that 3.(lie） below, they soon   ran into serious trouble. At one point, it seemed certain that their plane would crash. It could only get over the mountains if it rose to 10,000 feet. Byrd at once ordered his men to throw out two heavy food sacks. The plane was then able to rise and it cleared the mountains by 400 feet. Byrd now knew that he would be able to reach the South Pole which was 300 miles 10 away, for there were no more mountains 4. sight. The aircraft was able to fly over the endless white plains5. difficulty.