列举三种与肿瘤发生相关的病毒及其所致肿瘤。

Water in the World When people think of important resources, they think of oil, gas and coal. 26___ Many people in water-rich regions think that water can never be used up because the rain keeps falling. There are around 7 billion people on Earth. 27 ____ Less than a century ago, there were just 1 billion humans. There are more of us being born and most of us are living longer. We are using up far more of the world's resources at a faster rate than ever before. Water is the key to all life on Earth. 28__ The UN has stated that each person needs around 135 liters of water a day for a good quality of life. At the moment, the average amount of water we use is far larger in much of the world. If how we use water is not managed well enough, we could face increasing shortages in the future. This will lead to terrible conflict (冲突) over scarce water resources. 29__ There needs to be greater cooperation between the water-rich countries and the water-poor countries. 30__ If water is managed as a global resource and a basic human right, not as something for profits, then the supply can be managed well.

A.Without water, none of us would be here.

B.Water-rich regions may supply the extra water to water-poor regions. C.What they don't consider is our most important resource, water.

D.There are two types of water: salt water and fresh water.

E. This number is increasing by tens of millions every year.

F. If we can make better use of water, there should be enough water for everyone.