In the following paragraph, which methods are used to describe the problem: Global Warming? Global Warming is the extreme rise or increase in the temperature of the surface of the Earth. Global Warming is majorly the result of the increased Greenhouse effect. Because of this phenomenon, the water level of both sea and ocean has increased. Such a high increase in the level of water is unwanted and risky too as it can even result in a natural calamity like a flood.
选项：

A:Definition;
B:Comparison and contrast;
C:Exemplification;
D:Cause and effect