A、oxygen. B、ancient weather. C、carbon dioxide. D、temperature. BIt provides one of the clearest records of ancient weather．这句话是答

Scientists say they can tell what air and sea conditions were like hundreds of thousands of years ago. They say pieces of ice taken from Greenland provide such information.
    Scientists took the ice from more than one-and-a-half mile deep in huge masses of ice that float on the sea. That is the deepest scientists ever have drilled for ice. The ice represents 25,000 years of history. It provides one of the clearest records of ancient weather.
    European and American scientific teams have been studying ice from the same area to confirm each other’s findings. The scientists examine the ice that was formed each year. They measure the oxygen and carbon dioxide in the ice. These measurements tell about the year’s temperature.
     From these measurements, the scientific teams say that the past 10,000 years is the only period during which the weather has not changed very much. Before that time, they believe very large, sudden changes in the weather were common. The ice appears to show that at some periods, Earth’s weather changed from very hot to very cold in only ten years.