Three key facts about rising sea levels need to be pointed out to the world's politicians and planners: sea-level rise is now unavoidable, it will happen faster than most of us thought, and it will go on for a very long time. Even greenhouse gas emissions   stopped tomorrow, the oceans will continue to become larger as they get warm. The climate scientists estimate that sea-level rise may be in the range of 1 to 2 meters by 2100, with a small risk of an even greater rise. For many islands and low-lying regions, even small rises will cause disasters. But for most countries, the problem is what has been built on that land: New York, Sydney and Tokyo, to mention just a few cities. Unless something can be done, great areas of urban network will disappear under the waves. It will take a great engineering effort to protect these cities---an effort that may be beyond economies that have been brought to their knees. None of this means we should fear, and stop trying to forbid emissions. But together with these efforts, we need to start acting now and we must stop building in danger zones. Billions of dollars are being spent on constructing homes, offices and roads in _ coastal areas. For instance, the skyscrapers of Shanghai are being built on land that is merely 4 meters above sea level on average, and they are sinking under the weight of the buildings. Therefore, planning for new coastal developments is to go against reality. If we want to build a lasting heritage for our children, we should do so on the plentiful land that is in no danger from the sea. It is one of the effective ways to slow down climate change, and we should be acting on it now. What's the main purpose of this passage?
To explain why sea-level is rising. To tell us the danger of sea-level rise. To warn us of greenhouse gas emission. To discuss the disadvantage of building coastal cities.
Question: Three key facts about rising sea levels need to be pointed out to the world's politicians and planners: sea-level rise is now unavoidable, it will happen faster than most of us thought, and it will go on for a very long time. Even greenhouse gas emissions   stopped tomorrow, the oceans will continue to become larger as they get warm. The climate scientists estimate that sea-level rise may be in the range of 1 to 2 meters by 2100, with a small risk of an even greater rise. For many islands and low-lying regions, even small rises will cause disasters. But for most countries, the problem is what has been built on that land: New York, Sydney and Tokyo, to mention just a few cities. Unless something can be done, great areas of urban network will disappear under the waves. It will take a great engineering effort to protect these cities---an effort that may be beyond economies that have been brought to their knees. None of this means we should fear, and stop trying to forbid emissions. But together with these efforts, we need to start acting now and we must stop building in danger zones. Billions of dollars are being spent on constructing homes, offices and roads in _ coastal areas. For instance, the skyscrapers of Shanghai are being built on land that is merely 4 meters above sea level on average, and they are sinking under the weight of the buildings. Therefore, planning for new coastal developments is to go against reality. If we want to build a lasting heritage for our children, we should do so on the plentiful land that is in no danger from the sea. It is one of the effective ways to slow down climate change, and we should be acting on it now. What's the main purpose of this passage?
A. To explain why sea-level is rising.
B. To tell us the danger of sea-level rise.
C. To warn us of greenhouse gas emission.
D. To discuss the disadvantage of building coastal cities.
Answer: