问题 填空题

Part 1


·Read the fllowing passages, eight sentences have been removed from the article.
·For each gap (1-8) mark one letter (A-H) on the Answer Sheet.
·Do not mark any letter twice.
There’s a story in Texas about the rancher who complained when a well driller found oil instead of the water he had been sent to look for. "Cattle can’t drink that stuff!" the rancher cried.
That story is no longer funny. We are short of both oil and water, but the water shortage is worse. (1) And we are using water a great deal faster than it is being replaced. The replacement rate is dependent on rainfall (sometimes in the form of snow) to resupply rivers, lakes, and ground water. (2) Worse, droughts are occurring more frequently and are increasing in severity, not only in the United States but also abroad.
Even without droughts, rainfall is insufficient to maintain a balance. (3) So much water has been taken from the Colorado River by Arizona and California that Mexico has complained that those states have exceeded the U.S. share under a 1944 treaty on water-sharing. Southern Californians also have elaborated arrangements to transport water from the Pacific North west, which has it in abundance, to their area, which doesn’t have nearly enough to support its population. (4)
Short of a fanciful solution, the U.S. has two broad options, neither pleasant. We can conserve or we can produce. The former is inconvenient or worse: less irrigation (and thus less food), fewer swimming pools golf courses, and green lawns. (5) In the quantities necessary, this would probably require nuclear power. It is technically feasible, but expensive, and was considered 30 years ago as a joint U.S.-Mexican project in the Gulf of California to alleviate the Colorado river problem. As more of it is done, the cost could be expected to come down; and as we became more desperate for water, we would be more willing to pay the cost even if it didn’t come down. (6) This is an arrangement whereby large landowners would sell the groundwater under their land, for whatever the market would bear, to cities that might be hundreds of miles distant. This would involve the considerable cost of pipeline construction and would mean faster depletion of groundwater reserves. (7)
It’s a good bet that during the 21st century some new arrangements are going to have to be made about the nation’s — and the world’s — water supplies. These are likely to be neither cheap nor easy. They are more likely to be cheaper and easier if we have thought about them in advance. (8) We have been sued to choices of guns or butter. This one might be water or meat.
  • A. A century ago, a drought affected only farmers and perhaps inland navigation; now it affects everybody.
  • B. The Northwest is showing signs of getting tired of this drain.
  • C. It is not too soon to begin.
  • D. We cannot live without oil in the style to which we have become accustomed, but we cannot live at all without water.
  • E. Rivers are running dry, especially in the West.
  • F. It would also mean less food production.
  • G. A solution currently being advanced in west Texas is a concept called "Water Ranching".
  • H. The latter is expensive: desalinization of seawater.

答案

参考答案:E

解析: 第3段第1句提到,“即使没有旱情,降雨也不足以维持用水平衡”。水仍然是缺乏的。句3反映了由缺水导致的结果,后面提到因从河中取水引发的矛盾则是对这一问题的具体说明,因此E正确。

探究题

探究发光二极管的导电特性资料:

图a是一种重要的电子元件:晶体二极管,在电路中符号如图b.它是由半导体材料制成的,有两根引线,一根为正极,另一根为负极.有一种常见的二极管在导电时能发光,这种二极管叫做发光二极管(如图c),其电路符号如图d.二极管的导电性能很特殊,它只允许电流从它的正极流向负极,不允许从负极流向正极.这很像自行车气流从打气筒流向车胎.小丽和小明认真阅读完资料后,激起他们探究的欲望,决定合作实验验证二极管的这一特殊导电性小丽设计出如图1所示的电路.正准备连接电路时,小明提醒她这样的电路有问题,二极管可能会被烧坏,于是他们在电路中串上一滑动变阻器端.

(1)闭合开关前,滑片应位于 _________ (选填“a”或“b”)实验发现:

后来,小明无意中移动了滑片,眼尖的小丽发现电压表示数变大,电流表也有示数.对于这个现象他们很兴奋,猜想当电源正接时二极管导电性能是不是与它两端的电压大小有关呢?他们认真完成实验,并将记录的部分数据填入下表.

①当电源反接时(如图2),无论怎么移动滑片,电流表都 _________ 示数(选填“有”或“无”).

②当电源正接时(如图3),刚闭合开关,观察发现电流表无示数,二极管也不发光

后来,小明无意中移动了滑片,眼尖的小丽发现电压表示数变大,电流表也有示数.对于这个现象他们很兴奋,猜想当电源正接时二极管导电性能是不是与它两端的电压大小有关呢?他们认真完成实验,并将记录的部分数据填入下表.

(2)分析①和②现象,可知晶体二极管具有 _________ (填“单”或“双”)向导电的特性;

(3)根据以上实验数据用描点法,在所给的坐标纸上作出这个二极管的U﹣I图线;

(4)两人发现当二极管两端的正向电压达到1.9V后正常工作,则从表格中收集到的数据以及U﹣I图线可以看出这种二极管正常工作前后的导电情况有何区别? _________

(5)若电源电压为6V,当电流表示数为12.0mA时,滑动变阻器接入电路的阻值为 ____Ω

(6)使用发出两种色光的二极管,分别指示电动机正反两个转动方向,可以帮助操作人员及时发觉电动机转动方向是否符合需要.为此小丽和小明设计出符合需要的模拟电路.

[实验步骤]

(1)接通开关,二极管甲导通,发红光,电动机正转.

(2)调换电池组正、负极,接通开关,二极管乙导通,发绿光,电动机反转.

根据小丽和小明的设计思路,请你将二极管甲填入虚线框内.

填空题