Since 1960, the fast-growing town of Hotstone, Arizona, has drawn water from the Gray River, which feeds Lake Mudfish. If the town’s water use continues to grow at its present rate, in about 20 years the water level of Lake Mudfish will inevitably decrease to the point that it can no longer support its biologically fragile population offish.
The prediction above is based on which of the following assumptions ？（）
A. As the town’s water requirements grow, it will not be able to meet those requirements by drawing on water sources other than the Gray River.
B. Since 1960, the lake’s population of fish has become more biologically fragile.
C. The amount of water that the lake loses to evaporation each year will increase over the next two decades.
D. There are multiple sources of water besides the Gray River that feed into Lake Mudfish.
E. The town of Hotstone will be able to reverse its trend of increasing water use if it implements an aggressive water conservation program.
参考答案：A
解析：
If the town could meet its water requirements from sources other than the Gray River, then the depletion of Lake Mudfish would not necessarily be "inevitable;" since the prediction states that it is inevitable, statement A is an assumption upon which the prediction is based.