补体C3水平低下时,机体最易患的疾病是
A.肿瘤B.自身免疫病C.感染性疾病D.超敏反应E.以上都不是
参考答案:C
我们看到树叶是绿色的,是因为树叶只______ (选填“吸收”或“反射”)绿色光;同学们在教室的每个位置都能看清黑板上的字,这是光的______反射现象;如今许多建筑采用玻璃进行外墙装潢,这在美化城市的同时却造成了光污染,造成这种污染的主要原因是由于阳光在玻璃表面发生了______反射;镜面反射遵守光的反射定律,漫反射______(选填“遵守”或“不遵守”)光的反射定律.
Many people are surprised when they find the Internet(因特网)was set up in the 1960s. At that time, computers were large and expensive. Computer networks(网络) didn’t work well. If one computer in the network broke down, then the whole network stopped. So a new network system (系统) had to be set up. It should be good enough to be used by many different computers. If a part of the network was not working, information could be sent through another part. In this way computer network system would keep on working all the time. At first the Internet was only used by the government, but in the early 1970s,universities(大学) ,hospitals and banks were allowed(允许) to use it too. However, computers were still very expensive and the Internet was difficult to use. By the start of the 1990s, computers became cheaper and easier to use. Today it is easy to get on-line(上网) and it is said that millions of people use the Internet every day. Sending e-mail is more and more popular among students. The Internet has now become one of the most important parts of people’s life.
The word" information" may probably mean
A. letter B. message C. number