| The antigen-antibody immunological
reaction used to be regarded as typical of immunological responses. Antibodies
are proteins synthesized by specialized cells called plasma cells, which are
funned by lymphocytes (cells from the lymph system} when an antigen, a substance
foreign to the organism’s body, comes in contact with lymphocytes. Two important
manifestations of antigen- antibody immunity are lysis, the rapid physical
rupture of antigenic cells and the liberation of their contents into the
surrounding medium, and phagocytosis, a process in which antigenic particles are
engulfed by and very often digested by macrophages and polymorphs. The process
of lysis is executed by a complex and unstable blood constituent known as
complement, which will not work unless it is activated by a specific antibody;
the process of pbagocytosis is greatly facilitat A. proteins existed in specific group types B. proteins could have been shown to direct the synthesis of other proteins C. antigens were always destroyed by proteins D. antibodies were composed only of protein [单项选择]A. He used to live in the country. B. He used to work in the city.
C. He works in the city. D. He lives in the country. [单项选择]
Emotions Emotion is a feeling about or reaction to certain important events or thoughts. People enjoy feeling such pleasant emotions as love, happiness, and contentment. They often try to avoid feeling unpleasant emotions, such as loneliness, worry, and grief. Individuals communicate most of their emotions by means of words, a variety of sounds, facial expressions, and gestures. For example, anger causes many people to frown, make a fist, and yell. People learn ways of showing some of their emotions from members of their society, though heredity (遗传) may determine some emotional behavior. Research has shown that different isolated peoples show emotions by means of similar facial expressions. Charles Darwin, famous for the theory of natural selection, also studied emotion. Darwin said in 1872 that emotional behavior originally served both as an aid to survival and as a method of communicating intentions. According to the James-La A. overlooked internal physical reactions B. exaggerated the function of stimulating events C. faced a challenge from counter evidence D. offered a narrow interpretation of emotions [单项选择]
Weight on and off the Earth
We are so used to our life on the surface of the earth that it can be quite an effort for our mind to break free of all the ideas that we take for granted. Because we can feel that things are heavy, we think of "weight" as being a fixed quality in an object, but it is not really fixed at all. If you could take a one-pound packet of butter 4,000 miles out from the earth, it would weigh only a quarter of a pound. 我来回答: 提交
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