21. What is the real cause of the potential water crisis?

　　A) The world population is increasing faster and faster.

　　B) Half of the world’s water resources have been seriously polluted.

　　C) Humanity has not placed sufficient value on water resources.

　　D) Only half of the world’s water can be used.

　　22. As indicated in the passage, the water problem __________.

　　A) has been exaggerated by some experts in the field

　　B) is underestimated by government organizations at different levels

　　C) poses a challenge to the technology of building reservoirs

　　D) is already serious in certain parts of the world

　　23. According to the author, the water price should ___________.

　　A) correspond to its real value

　　B) be reduced to the minimum

　　C) stimulate domestic demand

　　D) take into account the occurrences of droughts

　　24. The author says that in some hot and dry areas it is advisable to __________.

　　A) build big lakes to store water

　　B) construct big pumping stations

　　C) channel water from nearby rivers to cropland

　　D) build small and cheap irrigation systems

　　25. In order to raise the efficiency of the water supply, measures should be taken to _______.

　　A) centralize the management of water resources

　　B) increase the sense of responsibility of agencies at all levels

　　C) guarantee full protection of the environment

　　D) encourage local and regional control of water resources

　　Passage Four

　　Questions 26 to 30 are based on the following passage:

　　We can see how the product life cycle works by looking at the introduction of instant coffee. When it was introduced, most people did not like it as well as “regular” coffee, and it took several years to gain general acceptance (introduction stage). At one point, though, instant coffee grew rapidly in popularity, and many brands were introduced (stage of rapid growth). After a while, people became attached to one brand and sales leveled off (stage of maturity). Sales went into a slight decline（衰退）when freeze-dried coffees were introduced (stage of decline).

　　The importance of the product life cycle to marketers is this: Different stages in the product life cycle call for different strategies. The goal is to extend product life so that sales and profits do not decline. One strategy is called market modification. It means that marketing managers look for new users and market sections. Did you know, for example, that the backpacks that so many students carry today were originally designed for the military?

　　Market modification also means searching for increased usage among present customers or going for a different market, such as senior citizens. A marketer may re-position the product to appeal to new market sections.

　　Another product extension strategy is called product modification. It involves changing product quality, features, or style to attract new users or more usage from present users. American auto manufacturers are using quality improvement as one way to recapture world markets. Note, also, how auto manufacturers once changed styles dramatically from year to year to keep demand from falling.