根据短文内容，选择最佳答案。    Do you know that in some parts of the world, people build temporary（暂时的）hotels made of snow and blocks（大块）of ice? These are known as ice hotels.
    Unlike usual hotels, all the rooms in the ice hotels are made of ice. In some ice hotels, even the glasses for drinks are made of ice blocks. So they only serve cold drinks. Also, hot food is not served in the ice hotels, but guests can eat hot food at places nearby.
    To keep warm, guests sleep in comfortable sleeping bags on ice blocks that are covered by mattresses（床垫）and reindeer skins（驯鹿皮）.
    There are some places in the ice hotels that are heated, such as the bathrooms. This is because, even though it is not as cold in the ice hotels as it is outdoors（在户外）, indoor temperatures are still very low.
    Perhaps the most interesting thing about the ice hotels is that they are rebuilt every year. They can be used only during the winter months. The ice hotels melt（融化）away when spring arrives. The ice blocks used to build these hotels are from nearby rivers. So, when the ice hotels melt away, they melt back into the rivers.