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磺胺类药物抑菌作用的机制是
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For centuries, explorers have risked their lives venturing into the unknown for reasons that were to varying degrees economic and nationalistic. Columbus went west to look for better trade routes to the Orient and to promote the greater glory of Spain, Lewis and Clark journeyed into the American wilderness to find out what the U. S. had acquired when it purchased Louisianan, and the Apollo astronauts rocketed to the moon in a dramatic show of technological muscle during the cold war.Although their missions blended commercial and political-military imperatives, the explorers involved all accomplished some significant science simply by going where no scientists had gone before.Today Mars looms as humanity"s next great terra incognita (未探明之地). And with doubtful prospects for a short-term financial return, with the cold war a rapidly fading memory and amid a growing emphasis on international cooperation in large space ventures, it is clear that imperatives other than profits or nationalism will have to compel human beings to leave their tracks on the planet"s reddish surface. Could it be that science, which has long played a minor role in exploration, is at last destined to take a leading role The question naturally invites a couple of others: are there experiment that only human could do on Mars Could those experiments provide insights profound enough to justify the expense of sending people across interplanetary spaceWith Mars the scientific stakes are arguably higher than they have ever been. The issue of whether life ever existed on the planet, and whether it persists to this day, has been highlighted by mounting evidence that the Red Planet once had abundant stable, liquid water and by the continuing controversy over suggestions that bacterial fossils rode to Earth on a meteorite (陨石) from Mars. A more conclusive answer about life on Mars, past or present, would give researchers invaluable data about the range of conditions under which a planet can generate the complex chemistry that leads to life. If it could be established that life arose independently on Mars and Earth, the finding would provide the first concrete clues in one of the deepest mysteries in all of science, the prevalence of life in the universe. According to the passage, the chief purpose of explorers in going to unknown places in the past was ______.
对于变构酶变构调节的叙述，恰当的是
pH与酶促反应速度关系的叙述，恰当的是
A wise man once said that the only thing necessary for the triumph of evil is for good men to do nothing. So, as a police officer, I have some urgent things to say to good people.Day after day my men and I struggle to hold back a tidal wave of crime. Something has gone terribly wrong with our once-proud American way of life. It has happened in the area of values. A key ingredient is disappearing, and I think I know what it is. accountability.Accountability isn"t hard to define. It means that every person is responsible for his or her actions and liable for their consequences.Of the many values that hold civilization together—honesty, kindness, and so on—accountability may be the most important of all. Without it, there can be no respect, no trust, no law—and, ultimately, no society.My job as a police officer is to impose accountability on people who refuse, or have never learned, to impose it on themselves. But as every policeman knows, external controls on people"s behavior are far less effective than internal restraints such as guilt, shame and embarrassment.Fortunately there are still communities—smaller towns, usually—where schools maintain discipline and where parents hold up standards that proclaim. "In this family certain things are not tolerated—they simply are not done!"Yet more and more, especially in our larger cities and suburbs, these inner restraints are loosening. Your typical robber has none. He considers your property his property; he takes what he wants, including your life if you enrage him.The main cause of this break-down is a radical shift in attitudes. Thirty years ago, if a crime was committed, society was considered the victim. Now, in a shocking reversal, it"s the criminal who is considered victimized, by his underprivileged upbringing, by the school that didn"t teach him to read, by the church that failed to reach him with moral guidance, by the parents who didn"t provide a stable home.I don"t believe it. Many others in equally disadvantaged circumstances choose not to engage in criminal activities. If we free the criminal, even partly, from accountability, we become a society of endless excuses where no one accepts responsibility for anything. We in America desperately need more people who believe that the person who commits a crime is the one responsible for it. What the wise man said suggests that ______.
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