Lake Vostok is potentially important to scientists because it________.

In Science, a theory is a reasonable explanation of observed events that are related. A theory 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. After a theory has been publicized, scientists design experiments to test the theory. If observations confirm the scientists’ predictions, the theory is supported. 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 arc 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 observations to test hypotheses. For without hypotheses, further investigation lacks purpose and direction. When hypotheses are confirmed, they are incorporated into theories. 

Which of the following is the main subject of the passage?

According to the passage, what way was used to eliminate the spread of smallpox?

Which one of the statements doesn’t refer to smallpox?

In the first paragraph, the word “elements” is closest in meaning to____.

The author discusses cows and horses in paragraph 3 in order to_________

In order to operate a computer, a student does not have to be _______

A Japanese construction company plans to create a huge independent city-state, akin to the legendary Atlantis, in the middle of the Pacific Ocean. The city, dubbed “Marinnation”, would have about one million inhabitants, two airports, and possibly even a space port. Marinnation, if built, would be a separate country but could serve as a home for international organisations such as the United Nations and the World Bank. Aside from the many political and social problems that would have to be solved, the engineering task envisaged is monumental. The initial stage requires the building of a circular dam eighteen miles in diameter attached to the sea bed in a relatively shallow place in international waters. Then, several hundred powerful pumps, operating for more than a year, would suck out the sea water from within the dam. When empty and dry, the area would have a city constructed on it. The actual land would be about 300 feet below the sea level. According to designers, the hardest task from an engineering point of view would be to ensure that the dam is leak proof and earthquake proof. If all goes well, it is hoped that Marinnation could be ready for habitation at the end of the second decade of the twenty-first century. Whether anyone would want to live in such an isolated and artificial community, however, will remain an open question until that time. 

According to the text, Marrination, when built, will be a(an)__________ city.

The word “this” as used in paragraph 2 refers to ___________.

The word ‘congested’ in paragraph 1 could best be replaced by ___.