题目

  Earlier this month, the Obama Administration called for increased protection of the world’s most southern continent, Antarctica. Scientists say climate change and human activity have increasingly led to the melting of massive pieces of Antarctic ice. The disappearance of ice will not only affect wildlife in the area such as seals and penguins. The melting will also cause oceans and seas around the world to rise.    This represents a major threat, especially to coastal areas. For example, the ancient city of Venice, Italy has long been threatened by rising sea levels. The situation is ma函数的定义域是    ．