题目

某生物兴趣小组为探究果实在发育过程中的体积变化，选择了 两朵 黄瓜雌花，坚持每天定时测量果实的体积，并绘制了果实体积变化曲线，据图回答(1)在曲线a中，幼果体积增长 是花的 迅速发育的结果，在此过程中 一般都逐渐凋落。（2）当黄瓜体积达到A点是，将它剖开发现有很多粒种子，这是因为每个子房里生有 （3）曲线b形成的原因是 （4）在大棚里种植黄瓜时，为避免出现曲线b的现象，可以采取 的措施。Humanity uses a little less than half the water available worldwide. Yet occurrences of shortages and droughts (干旱) are causing famine and distress in some areas, and industrial and agricultural by-products are polluting water supplies. Since the world's population is expected to double in the next 50 years, many experts think we are on the edge of a widespread water crisis. 　 But that doesn't have to be the outcome. Water shortages do not have to trouble the world---if we start valuing water more than we did in the past. Just as we began to appreciate petroleum more after the 1970s oil crises, today we must start looking at water from a fresh economic perspective. We can no longer afford to consider water a virtually free resource of which we can use as much as we like in any way we want. 　 Instead, for all uses except the domestic demand of the poor, governments should price water to reflect its actual value. This means charging a fee for the water itself as well as for the supply costs. 　 Governments should also protect this resource by providing water in more economically and environmentally sound (健康的) ways. For example, often the cheapest way to provide irrigation water in the dry tropics is through small-scale projects, such as gathering rainfall in depressions (凹地) and pumping it to nearby cropland. 　 No matter what steps governments take to provide water more efficiently, they must change their institutional and legal approaches to water use. Rather than spread control among hundreds or even thousands of local, regional, and national agencies that watch various aspects of water use, countries should set up central authorities to coordinate (调整) water policy. What is the real cause of the potentials water crisis. 　　A. Only half of the world's water can be used. 　　B. The world population is increasing faster and faster. 　　C. Half of the world's water resources have been seriously polluted. 　　D. Humanity has not placed enough value on water resources. As is indicated in the passage, the water problem _________ . A. is already serious in certain parts of the world. B. has been exaggerated by some experts in the field 　　C. poses a challenge to the technology of building reservoirs(水库) 　　D. is underestimated by government organizations at different levels According to the author, the water price should _______ . 　　A. be reduced to the minimum        B. stimulate domestic demand 　　C. go with its real value             D. take into account the occurrences of droughts In order to raise the efficiency of the water supply, measures should be taken to ______ . 　　A. guarantee full protection of the environment 　　B. centralize the management of water resources 　　C. increase the sense of responsibility of agencies at all levels D. encourage local and regional water resources