[填空题] Water is tasteless, odorless, and nearly colorless (it has a slight hint of blue). It is a 【B1】 that is essential to all known forms of life in its pure form. Water is 【B2】 on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also 【B3】 clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is 【B4】 moving through the cycle involving evaporation, precipitation , and runoff to the sea. Water fit for human 【B5】 is called potable water. This natural resource is becoming 【B6】 in certain places as human population in those places increases, and its availability is a major social and economic 【B7】 . Drinking water is water that is intended to be drunk by humans. Water of 【B8】 quality to serve as drinking water is called potable water whether it is used as such or not. Although most fresh water sources are drinkable 【B9】 humans, they can be a disease vector or cause long-term health problems if they do not 【B1
A. A．depends on
B．depends
C．depending on
D．independent from