A water pump can not supply water after startingIt may be ca

According to the last paragraph, the fourth way is "of a different kind" because（ ）

[A] the first three ways can increase the water supply, while the fourth one can't

[B] the first three ways can make a better use of water, while the fourth one can't

[C] the first three ways is technology-based, while the fourth one is market-based

[D] the first three ways can't balance the supply and demand of water, while the fourth one can

A centrifugal pump may fail to deliver water when first started if the ______.

A.water seal pipe is plugged

B.pump is not primed

C.seal ring is properly located

D.impeller is flooded

E

The need to feed a growing population is putting much pressure on the world’s supply of water. With 97% of the world’s water too salty to be drunk or used in agriculture, the worldwide supply of water needs careful management, especially in agriculture. Although the idea of a water shortage（短缺）seems strange to someone fortunate enough to live in a high rainfull country, many of the world’s agricultural industries experience constant water shortages.

Although dams can be built to store water for agricultural use in dry areas and dry seaons, the costs of water redistribution(重新分配)are very high. Notonly is there the cost of the engineering itself, but there is also an environmental cost to be considered. Where valleys(山谷)are flooded to create dams, houses are lost and wildlife homes destroyed. Besides, water many flow easily through pipes to fields,but it cannot be transported from one side of the world to the other. Each country must therefore rely on the management of its own water to supply its farming requirements.

This is particularly troubling ro countries with agricultural industries in areas dependent on irrigation（灌溉）. In Texas, farmers’ overuse of irrigation water be resulted in a 25% redcution of the water stores. In the Central Valley area of south eastern USA, a huge water engineering project provided water for farming in dry vallege, but much of the water use has been poorly managed.

Saudi Arabia’s attempts to grow wheat in desert areas have been the pumping of huge quantities of irrigation water from underground reserves. Because there is no rainfall in these areas, such reserves can only decrease, and it is believed that fifty years of pumping will see them run dry.

72. From the first two paragraphs we learnt that _______.

A.much of the world’s water is available for use

B.people in high rainfll countries feel lucky

C.the costs of water redistribution should be considered

D.water can be easily carried through pipes across the world

If the feed pump for an auxiliary boiler fails to deliver the feed water to the boiler, the cause may be ______.

A.high steam pressure in the boiler

B.abnormally high feed-water temperature

C.abnormally high boiler water temperature

D.steam demand exceeding feed pump capacity

The text is mainly about .

A.water supply and increasing population

B.water use management and agriculture

C.water redistribution and wildlife protection

D.water shornages and environmental protection.