高考Using his skis, Nicholas built a snow cave.
高考He followed his tracks and returned to the snow cave, because without shelter, he could die that night.
高考A few daring survived, though, along with a few stay-in-the-cave types.
高考Not knowing how much longer he could last, Nicholas did the only thing he could — he huddled in his cave and slept.
六级As a measure to counter future shortages, the American government decided to establish a stockpile of oil in caves underground
六级Stored underground in large salt caves in Louisiana, this stockpile is called the Strategic Petroleum Reserve, and currently contains over 600 million barrels of oil, roughly equivalent to one month's supply.