开关电源的一个缺点是要求滤波电容的容量比较大才能得到良好的滤_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题判断题

开关电源的一个缺点是要求滤波电容的容量比较大才能得到良好的滤波效果。

答案

参考答案：错

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.

单项选择题

下列关于脑肿瘤实验室诊断不正确的是（）

A.β-葡萄糖苷酶下降

B.酸性磷酸酶增高

C.CK及同工酶增高

D.核糖核酸酶增高

E.AST增高