题目

关于锋面对我国天气影响的叙述，正确的是(    ) ①我国一些灾害性天气大多与锋面有关  ②我国的降水大多集中在夏季，因此我国的天气主要受暖锋活动影响  ③我国夏季也有冷锋活动  ④影响我国天气的锋面主要是冷锋 A．①②④      B．①③④        C．②③④         D．①②③ 答案：BWe keep our money in a bank for use when we need it.Doctors keep quantities of  1   kinds of blood in blood-banks for use when  2   .Blood can be  3   for about 3 weeks in a good state. If it is dried, part of it can be kept longer. So there is no  4   for the doctor to wait for a  5   of the right blood-group to come forward to offer his blood. The blood is  6   in the blood-bank for the transfusion(输血).More and more blood is being  7   in this way, and there is not always  8   .In England we sometimes hear a  9   in the streets of a town coming from a car which is standing on the  13   , and the time to go. The giving of blood for this purpose does not  14   a blood-donor(献血者)in good  15   .The doctors know  16   blood to take from the body, and the kind and helpful person does not  17   ill. Usually enough people come to offer their blood, and usually the donor  18   knows  19   he helps and whose life he  20  .1．