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　　With the prospect of coal and petroleum supplies depleted and with air pollution becoming an increasing concern, the major countries of the world are seeking alternate sources of energy. If a means to obtain energy from water, especially from the ocean, can be effected economically, it would furnish a never ending supply of energy, since 70% of the earth′s surface is ocean and another 10% is fresh water in rivers and lakes.
　　From the beginning of time man has used water power as a source of work— waterfalls and dams —but these are fresh water sources and are landlocked. The seas have contributed little or nothing in the way of power.
　　The use of temperature variation between currents is one area of exploration. Ocean water is heated by the sun near the equator and drawn by the rotation of the earth toward the poles, where it cools and drops toward the ocean floor and starts its journey back toward the equator. The differential（微分）between the two currents is 35 degrees to 45 degrees Fahrenheit and to use it the scientists must find the places where they run near land and are not too far away from each other. One area that meets these requirements is the Caribbean Sea.
　　Oceans also offer wave power, tides and the chemical propensities（倾向）of salt water as potential sources of energy. All these uses are theoretically possible. 　　
　　Britain′s Department of Energy is interested in wave power, using a string of “tear drop” devices that depend on very active wave areas and 100 feet depths. In addition to this, the British are working on a method that the Japanese have already put into practical use on a small scale for powering their navigational buoys. This method is called an oscillating（震荡）water column and rides the waves with a series of cylinders having one way air valves. Wave movement produces air under pressure that has only one escape route— to a turbine （涡轮）that powers a generator.
　　1. The word “depleted” (Line 2, Para.1) possibly means “______”.
　　A．exhausted
　　B．discarded
　　C．polluted
　　D．disappeared
　　2. According to the first two paragraphs, ______.
　　A．the use of water is a completely new concept
　　B．the sea has long been used as a way of power
　　C．water is a source of energy far more economical than any other energies
　　D．water, if properly handled, may present a promising solution to energy crisis
　　3. According to the passage, the Caribbean Sea is the place where ______.
　　A．two currents of different temperatures run near to each other and not far away from land
　　B．two currents of different temperatures run near to each other but far away from land
　　C．the ocean water is heated by the sun
　　D．the ocean water gets cool
　　4. We can learn from the passage that ______.
　　A．as far as energy source is concerned, salt water is useless because of its chemical properties
　　B．the working principle of an vibrating water column is to use water as a direct power driving a generator
　　C．Britain is pursuing a method that the Japanese have already put into practice
　　D．Britain is the most advanced country in developing new energy source
　　5. What is the passage mainly about?
　　A．Energy crisis.
　　B．Water as a possible solution to energy crisis.
　　C．History of the use of water as a source of work energy.
　　D．Properties of water.