题目

人站在小车上尽力水平推铅球，设人和小车的总质量为M，铅球的质量为m．若小车固定不动时，铅球被推出的速度为v0，那么，当地面光滑小车能自由移动时，铅球被水平推出的速度大小是                             （    ）        A．v0                                              B．v0                     C．v0              D．v0 阅读文章，选出问题的最佳选项。 　　We can achieve knowledge either actively or passively(被动地)．We achieve it actively by direct experience, by testing and proving an idea, or by reasoning． 　　We achieve knowledge passively by being told by someone else．Most of the learning that takes place in the classroom and the kind that happens when we watch TV or read newspapers or magazines is passive．Conditioned as we are to passive learning, it's not surprising that we depend on it in our everyday communication with friends and co－workers· 　　Unfortunately, passive learning has a serious problem．It makes us tend to accept what we are told even when it is little more than hearsay and rumor(谣言)． 　　Did you ever play the game Rumor? It begins when one person writes down a message but doesn't show it to anyone．Then the person whispers it, word for word, to another person．That person, in turn, whispers it to still another, and so on, through all the people playing the game．The last person writes down the message word for word as he or she hears it．Then the two written statements are compared Typically, the original message has changed． 　　That's what happens in daily life．The simple fact that people repeat a story in their own words changes the story．Then, too, most people listen imperfectly．And many enjoy adding their own creative touch to a story, trying to improve on it, stamping(打上标记)it with their own personal style．Yet those who hear it think they know． 　　This process is also found among scholars and authors：A statement of opinion by one writer may be re－stated as fact by another, who may in turn be quoted(引用)by yet another; and this process may continue, unless it occurs to someone to question the facts on which the original writer based his opinion or to challenge the interpretation he placed upon those facts． (1) According to the passage, passive learning may occur in ________． [　　] A． doing a medical experiment B． solving a math problem C． visiting an exhibition D． doing scientific reasoning (2) The underlined word “it” in Paragraph 2 refers to ________． [　　] A． active learning B． knowledge C． communication D． passive learning (3) The author mentions the game Rumor to show that ________． [　　] A． a message may be changed when being passed on B． a message should be delivered in different ways C． people may have problems with their sense of hearing D． people tend not to believe in what they know as rumor (4) What can we infer from the passage? [　　] A． Active learning is less important． B． Passive learning may not be reliable． C． Active learning occurs more frequently． D． Passive learning is not found among scholars．