[单项选择] Recent research has claimed that an excess of positive ions in the air can 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 between the positive and the negative charges (电荷). But sometimes this 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 fibres, 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 b
A. near a pond with a water pump
B. close to a slowly flowing river
C. high on some barren mountains
D. near a fountain