Passage 3
　　In science, a theory is a reasonable explanation of observed events that are related. A the-ory often involves an imaginary model that helps scientists picture the way an observed event could be produced. A good example of this is found in the kinetic molecular theory, in which gases are pictured as being made up of many small particles that are in constant motion. 
　　A useful theory, in addition to explaining past observations, helps to predict events that have not as yet been observed. After a theory has been publicized, scientists design experi-merits to test the theory. If observations confirm the scientists’ predictions, the theory is sup-ported. If observations do not confirm the predictions, the scientists must search further. There may be a fault in the experiment, or the theory may have to be revised or rejected.
　　Science involves imagination and creative thinking as well as collecting information and performing experiments. Facts by themselves are not science. As the mathematician Jules Henri Poincare said: "Science is built with facts just as a house is built with bricks, but a collection of facts cannot be called science any more than a pile of bricks can be called a house." Most scientists start an investigation by finding out what other scientists have learned about a particular problem. After known facts have been gathered, the scientist comes to the part of the investigation that requires considerable imagination. Possible solutions to the problem are formulated. These possible solutions are called hypotheses. 
　　In a way, any hypothesis is a leap into the unknown. It extends the scientist’s thinking beyond the known facts. The scientist plans experiments, performs calculations, and makes ob-servations to test hypotheses. For without hypotheses, further investigation lacks purpose and direction. When hypotheses are confirmed, they are incorporated into theories.
　　11. The word "this" in the 3rd sentence in paragraph 1 refers to ______.
　　A) a good example 
　　B) an imaginary model
　　C) the kinetic molecular theory 
　　D) an observed event
　　12. Bricks are mentioned in the 3rd paragraph to indicate how ____.
　　A) mathematicians approach science
　　B) building a house is like performing experiments
　　C) science is more than a collection of facts
　　D) scientific experiments have led to improved technology
　　13. In the last paragraph, the author refers to a hypothesis as "a leap into the unknown" in or- der to show that hypotheses ______.
　　A) are sometimes ill-conceived 
　　B) can lead to dangerous results
　　C) go beyond available facts 
　　D) require effort to formulate
　　14. What is a major function of hypotheses as implied in the last paragraph7
　　A) Sifting through known facts.
　　B) Communicating a scientist’s thoughts to others.
　　C) Providing direction for scientific research.
　　D) Linking together different theories.
　　15. Which of the following statements is supported by the passage?
　　A) Theories are simply imaginary models of past events.
　　B) It is better to revise a hypothesis than to reject it.
　　C) A scientist’s most difficult task is testing hypotheses.
　　D) A good scientist needs to be creative.
　　Passage 3

　　文章大意：

　　这篇文章从定义、作用及产生过程几方面阐述了科学理论。科学理论是对观察到的相关事物的解释。经常包括一个想象的模式来帮助科学家想象事物的产生过程。而一个实用的理论，不仅可以解释以往的观察，还可以帮助预测等待观察的事物。观察又可以验证一个理论是否正确。科学除了包括收集信息和做实验，还需要创造性的思考，然后形成可能的问题解决方法，即假设。假设总是朝着未知领域前进一步，它拓宽了科学家的视野，经过验证后的假设就变成了理论。

　　答案解析：

　　[11]B第三句话中的代词“this'’指代前一句提到的“an imaginary model"。因为这个例子就是要说明在动力分子理论中，气体被描绘成由许多不停运动的小分子所组成，即前句中“理论常包含一个想象模式来帮助科学家描绘事件的产生过程。”

　　[12]C第三段最后一句中“科学是由事实构成的，就象房屋是由砖建成的。但是事实堆积起来并不能成为科学，这比用砖块搭房子复杂得多”。因此说科学并不是简单的堆砌事实。

　　[13]C最后一段第二句话，“假设”使科学家的思想可以超越已知事实。

　　[14]C最后一段第四句话，若没有假设，更深入的调查就会缺少目标和方向。所假设的一个主要作用就是给科研提供方向。

　　[15]D第二段第一句说明理论不仅可以解释以往的观察，还可以帮助预测还未观察到的。

　　因此排除A。第二段最后两句，如果观察不能证实预测，那么说明实验有错或理论可能应被修改或推翻，因此排除B。而C在文章中没有涉及。根据第三段最后一句话，科学需要想象力和创造性思考，可以得出D为正确答案。