Recent research had claimed that an excess of positive ions in the air could have an ill effect on people's physical or psychological health. What are positive ions? Well, the air is full of ions, electrically charged particles, and generally there is a rough balancE.If the balance becomes disturbed and a larger proportion of positive ions are founD.This happens naturally before thunderstorms, earthquakes or when winds such as the Mistral, Foehn, Hamsin or Sharav are blowing in certain countries. Or it can be caused by a build-up of static electricity indoors from carpets or clothing made of man-made fibers, or from TV sets, duplicators or computer display screens. When a large number of positive ions are present in the air many people experience unpleasant effects such as headaches, fatigue, irritability, and some particularly sensitive people suffer nausea or even mental disturbancE.Animals are also found to be affected, particularly before earthquakes: snakes have been observed to come out of hibernation, rats to flee from their burrows, dogs howl and cats jump about unaccountably. This has led the US Geographical Survey to fund a network of volunteers to watch animals in an effort to foresee such disasters before they hit vulnerable areas such as CaliforniA. Conversely, when large numbers of negative ions are present, then people have a feeling of well-being. Natural conditions that produce these large amounts are near the sea, close to waterfalls or fountains, or m any place where water is sprayed, or forms a spray. This probably accounts for the beneficial effect of a holiday by the sea, or in the mountains with tumbling streams or waterfalls. To increase the supply of negative ions indoors, some scientists-recommend the use of ionisers: small portable machines that generate negative ions. They claim that ionisers not only clean and refresh the air but also improve the health of people sensitive to excess positive ions. Of course, there are the detractors, other scientists, who dismiss such claims and are skeptical about negative or positive in research. Therefore people can only make up their own minds by observing the effects on themselves, or on others, of a negative rich or poor environment. After all, it is debatable whether depending on seismic readings to anticipate earthquakes is more effective than watching the cat. What effect does excessive positive ions have on some people? A.They think they are maD. B.They feel very tireD. C.They become violently sick. D.They are too tired to do anything.
A.B. C. D. What E.They F. B.They G. C.They H. D.They
B 解析：文章第二段第一句谈到了大量的正离子会使人感到疲惫不堪，甚至出现恶心和精神错乱等症状，所以B“使人感到疲惫不堪”是正确答案。sensitive people可能会精神错乱，但A“他们觉得自己疯了”夸大了事实。他们可能会生病，但C中violently一词显然过于严重。D“累得什么也干不了”在文中找不到根据。