如图所示，A、B为真空中的两个电荷，O为A、B连线的中点，MN为A、B连线的中垂线，电场线的分布关于MN对称。以下判断正确的是
A.A、B为等量异种电荷
B.M点电势高于O点电势
C.M点场强小于O点场强
D.正检验电荷在M点的电势能大于O点的电势能
AC
题目分析：电场线是从正电荷或者无穷远出发出，到负电荷或无穷远处为止．根据电场线与等势线垂直，判断电势的高低．在两等量异号电荷连线的中垂线上，中间点电场强度最大，也可以从电场线的疏密判断场强的大小．
根据电场线的特点，从正电荷出发到负电荷终止可以判断，A、B是两个等量异种电荷．故A正确，
根据平行四边形定则，对中垂线上的场强进行合成，知中垂线上每点的电场方向都水平向右，中垂线和电场线垂直，所以中垂线为等势线，所以M点的电势等于O点的电势．B错误，正电荷在电势高的地方电势能大，故D正确，
在两等量异号电荷连线的中垂线上，中间点电场强度最大，也可以从电场线的疏密判断，所以O点的电场强度比M点的电场强度大，故C正确．
故选ACD
Passage Four
| "Much of the sickness and death attributed to the major communicable (可传染的) diseases is in fact caused by malnutrition (营养不良) which makes the body less able to withstand infections when they strike," said Dr. Hiroshi Nakajima, Director-General of the World Health Organization (WHO). "At the same time," he added, "in developing countries today, malnutrition is the cause of 174 million children under five years of age being underweight, and 230 million being stunted in their growth. Such figures represent deprivation, suffering and wasted human potential on a scale that is unacceptable from every point of view. Whether we think interms of humanitarian concern, common justice or development needs, they demand a response, both from national governments and from the international community. " WHO, working closely with its member states, other United Nations agencies and nongovernmental organizations, is focusing on major crippling (致残的) forms of malnutrition, such as protein-energy malnutrition, vitamin A deficiency (缺乏，不足). At the end of January 1996, 98 countries had national plans of action for nutrition and 41 countries had one under preparation, in keeping with their commitments made at the International Conference on Nutrition in Rome December 1992. The global situation, however, remains grim. Over 800 million people around the world still cannot meet basic needs for energy and protein, more than two thousand million people lack essential micro-nutrients, and hundreds of millions suffer from diseases caused by unsafe food or unbalanced diets. It is now recognized that 6.6 million out of the estimated 12.2 million deaths annually among children under five—or 54% of young child mortality (死亡率) in developing countries—is associated with malnutrition. In addition to the human suffering, the loss in human potential translates into social and economic costs that no country can afford. In 1990, only 53 developing countries had reliable data on the number of young children under weight; by 1995, 97 countries had such data, nearly all of which included information on stunting and wasting. In some regions, such as sub-Saharan Africa and south Asia, stagnation of nutritional improvement combined with a rapid rise in population has resulted in an actual increase in the total number of malnourished children. Currently, over two-thirds of the world’s malnourished children live in Asia (especially south Asia), followed by Africa and Latin America. |
It can be inferred from Para. 2 that ______ .
A．WHO does not pay enough attention to minor forms of malnutrition
B．the international community reached a consensus to fight malnutrition in 1992
C．WHO member countries have well fulfilled their promise for nutrition plans
D．the number of deaths caused by malnutrition has been increasing since 1992