题目内容
根据短文内容，从下边的A—F选项中选出能概括每一段主题的最佳选项。选项中有一项为多余选项。
A . The different structure of blue holes.
B. Why scientists are interested in blue holes.
C. How a blue hole comes into being.
D. Blue holes exploring is becoming popular.
E. Rules to obey when diving into blue holes.
F. The general definition of a blue hole.
61. ______________
A blue hole is a flooded sea cave with a hole that opens up at the land's surface. These cave systems form in carbonate rock, often on islands. Some blue holes have very special rock formations and water chemistry. Far below sea level, they contain some of the harshest environments on Earth, with no oxygen and no light. Yet these areas are filled with life forms that have adapted to the extreme conditions.
62. ____________
Blue holes get their name from the color some have when seen from the air. The color is usually a reflection of the sky on the water. Blue holes are the result of erosion in which water breaks down rock. Rain falling thousands of years ago contained chemicals which slowly wore away at the limestone landmass. These holes later filled with sea water as the sea level changed. The rising and falling of sea levels and the mixture of salt and fresh water further wore away at these cave formations.
63. ____________
These flooded cave systems can be found in the ocean, or they can be found inland. Ocean caves are affected by tides, so they always have water movement. But blue holes on land are very still. They have several layers of water, chemicals, and bacteria. The top layer of fresh water comes from rainfall. This layer acts like a cap on top of the layered mixture, and keeps out oxygen from the atmosphere. The fresh water floats on a denser layer of saltwater. Underneath this is a layer of poisonous hydrogen sulfide, produced by bacteria living in the water. Underneath this layer is anoxic seawater -- water that does not contain any oxygen.
64. ___________
Information gathered from these blue holes is helping scientists to increase their understanding of biology, archaeology and geology. But exploring these blue hole environments brings danger as well as discovery. Scientists are interested in these caves because oxygen-free conditions there are similar to those on Earth long ago, before oxygen existed on our planet. But there are many difficulties involved in diving into blue holes.
65. ___________
One reason blue holes have not been fully explored is that they can be extremely dangerous. There are many safety rules that divers must follow to help ensure their survival. First, divers must have training and experience to swim in these caves. Divers who explore a cave for the first time must establish a thin rope called a guideline. This line helps them to safely enter and exit the cave without getting lost.
FCABE
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根据短文内容，从下边的A-F选项中选出能概括每一段主题的最佳选项。选项中有一些为多余项。
| A. Drug overuse and its consequence B. The problem of drug overuse in America C. Benefits of medicine and its wise use D Female drug overuse with reference to that of males E Misuse of medicine among the young generation F. Improper use of medicine among senior citizens |
Nowadays. millions of people misuse and even overuse pain medications and other drugs. Research by the American National Institute on Drug Abuse (NIDA, 1999) shows that around 2% of the population over age 12 were using drugs non-medically.
NIDA views medications as a powerful force for good in the contemporary world. They reduce and remove pain for millions of people suffering from illness and disease. They make it possible for doctors to perform complicated surgery to save lives. Many people afflicted by serious medical conditions are able to control their symptoms and become active, contributing citizens. NIDA points out that most individuals who take these drugs use them in a responsible.
Nevertheless, overuse of drugs such as opioids, central nervous system (CNS) depressants and stimulants does lead to harmful reliance in some people and is therefore becoming a serious public health concern. Although this abuse affects many people worldwide, particular trends of concern to the medical profession in the US appear among older adults, teenagers arid women.
64.
Though it may be a surprise to many, the misuse of medications may be the most common form of drug abuse among the elderly. Dr Kenneth Schrader of Duke University, North Carolina states that although the elderly represent about 13% of the US population, those aged 65 and over account for the consumption of one third of all drugs. People in this age group use medications roughly three times more than the general population and have poorer compliance with instruction for use. In another study of elderly patients admitted to treatment programs, 70% were women who had overused medicines.
Unfortunately, this trend among women does not only affect those aged over 65. In general, among women and men who are using either an anti-anxiety drug or a sedative, women are twice as likely to become addicted. In addition, statistics compiled for 12-17 year olds show that teenage girls are more likely than teenage boys to begin overusing psychotherapeutic medication such as painkillers, tranquillizers, stimulants and sedatives.