题目

若P是平面外一点，A为平面内一点，为平面的一个法向量，则点P到平面的距离是 A．          B．       C．       D． 答案：C 【解析】 试题分析：设与的夹角为，则点P到平面的距离为=，故C正确. 考点：空间向量、向量的运算.It's interesting that the arrival of snow has effect on people in different countries. For some countries it is an important happening to celebrate each year, while for others a catastrophe(灾害) or even a wonder.?But there are countries between these two kinds that normally expect snow some time over-the winter months, but never receive snow regularly or in the same quantities every year. Britain is one of them, for which the arrival of snow quite simply causes problems. Within hours of the first snowfalls, however light, roads are blocked; trains and buses have to stop in the middle of the way. Normal communication is affected as well: telephone calls become difficult and the post immediately takes more time than usual. And almost within hours, there are also certain shortages—bread, vegetables and other things—not because all these things can no longer be produced or sent to shops, but mainly because people are frightened and go out and store up with food and so on just for fear that something bad should happen.?But why does snow have this effect? After all, the Swiss, the Austrians and the Canadians don't have such problems. It is simple because there is not enough planning and preparation. We need money to buy equipment to deal with snow and ice. To keep the roads clear, for example, requires snow-ploughs(扫雪机) and machines to spread salt. The reason why a country like Britain does not buy snow-ploughs is that they are used for a few days in any one year, and the money could be more useful in other things such as hospital, education, helping the old.?1.According to the writer, Britain is a country _______.?A.which has regular snowB.which is not well prepared for snow?C.for which snow is a catastropheD.for which snow is a wonder?2.After a few hours' snowing there are often some shortages of food because _______.?A.shops have closed downB.people buy as much as they can?C.farmers cannot produce any moreD.people eat more vegetables in winter?3.The words “two kinds” in the passage mean the countries _______.?A.which have weather as yearly happening to celebrate or as rare (少见) weather?B.which either have heavy snow or light snow?C.to which snow either causes problems or no problems?D.which either have snow-ploughs or no snow-ploughs