Read the following article and select the best answer. Article: Can you remember a morning when you've woken up to the ring of your alarm clock and wished you could stay in bed? You haven't slept well, your hair is a mess. Worse, you can't stop yawning. Yawning is universal to humans and many animals. Cats, dogs and fish yawn just like humans do! Yawning is an involuntary(,) action during which you open your mouth and breathe deeply. The average duration of a yawn is about 6 seconds. The purpose and cause of yawning are still a mystery. Scientists are not sure what causes a yawn. People yawn when they are tired or bored, but they also yawn when they aren't. There are many ideas explaining why we yawn. One idea is that yawning is a way for the body to become more alert by taking in more oxygen. A yawn increases the heart rate, forces carbon dioxide out of the lungs and blood stream, and brings oxygen to the brain. But one study showed that volunteers given a lot of oxygen did not yawn any less than before, while those given a lot of carbon dioxide did not yawn more. Another idea is that early humans used yawning as a form of communication. If one decided it was time to sleep, they would tell the others by yawning and they would do it in return to show they agreed. A third explanation comes from psychology professor Gordon Gallup of University at Albany in New York. He said that as people yawn, they cool off their brains. "Brains are like computers." he said. "They only operate efficiently and effectively when they're cool. Many things connected to yawning, like being tired, make the brain hot, and yawning can reduce the heat." Scientists have sent people into space, and created terrible nuclear weapons, but there are lots of seemingly simple things, such as why we yawn, or hiccup , that they can't figure out. Next time you are in class in the morning, let out a big yawn and watch to see how many of your classmates yawn in response! Question: Which is not among the possible reasons for yawning mentioned in the passage? - A way to show that you feel hot. - A way to get rid of carbon dioxide. - A way to cool off your brain. - A way to communicate.
A way to show that you feel hot.

Read the following article and select the best answer. Article: WASHINGTON--Two-thirds of the world's polar bear population could be gone by 2050 if predictions of melting sea ice hold true, the US Geological Survey reported on Friday. The fate of polar bears could be even worse than that estimate, because sea ice in the Arctic might be disappearing faster than the available computer models predict, the geological survey said in a report aimed at determining whether the big white bear should be listed as a threatened species. "There is a definite link between changes in the sea ice and the welfare of polar bears," said Steve Amstrup, who led the research team. He says Arctic sea ice is already at the lowest this year and is expected to retreat farther this month. That means that polar bears--some 16,000 of them -- will disappear by 2050 from parts of the Arctic where sea ice is melting most rapidly, along the north coasts of Alaska and Russia, researchers said in a telephone briefing . Other polar bears could survive beyond that date but many of those could be gone by 2100, Amstrup said. By this century's end, the only polar bears left might live in the Canadian Arctic islands and along the west coast of Greenland. "It is likely to result in loss of approximately two-thirds of the world's current polar bear population by the mid 21st century," the report's executive summary said. "Because the observed trajectory of Arctic sea ice decline appears to be underestimated by currently available models, this assessment of future polar bear status may be conservative ." In January, the US Fish and Wildlife Service proposed listing the polar bear as a threatened species, noting polar bears depend on sea ice as a platform to hunt seals, their main food. Without enough sea ice, polar bears would be forced onto land, but they are poor hunters once they get out of the water and ice, the researchers said. The bears' disappearance would probably take place as young cubs failed to survive to adulthood and females were unable to reproduce successfully. Question: What was the US Geological Survey intended to do? - To determine whether the polar bear was in danger. - To measure how fast the sea ice melts in the Arctic. - To check the predictions of the computer models. - To find out the exact number of the polar bear.
To determine whether the polar bear was in danger.

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Read the following article and select the best answer. Article: The earth is not the only body that travels around the sun. With it are eight other planets, fellow members of the sun's family. Two of them, Mercury and Venus, are nearer while the other six, namely Mars, Jupiter, Saturn, Uranus, Neptune and Pluto, also in their given order from the sun, are farther from the sun than the earth is. The farther they are, the longer trips they make around the sun. People noticed long ago that these traveling bodies moved around in the sky in definite paths. It is a force called gravity that holds them in their paths. We know that every little bit of matter in the universe pulls upon every other bit of matter. The pull between two bodies is proportional to the product of their masses. Because the sun is so large the pull between the sun and the planets are thus great. If it were not for this pull, the planets would fly off into space. In the same way there exists a pull between the earth and the moon, which keeps the moon traveling in its orbit around our planet, the earth. Gravity holds you to its surface, and pulls back to it the ball which you throw into the air. Of course the ball also pulls on the larger earth but the earth is so much larger that the pull is not noticed. Now remember that large bodies exert a greater pull than smaller ones which contain less material. But each object in the universe, no matter how small, pulls on all other objects to some degree. Question: From the passage we can see _ - all the objects, big or small, must exert the same pull on one another - large objects exert the same pull on anybody as small objects - small objects exert the same on large ones - each object in the universe exerts a pull on all other objects
(Answer)
each object in the universe exerts a pull on all other objects