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In this task, you're given an article and an answer. Your task is to generate the question for the answer based on the given article.
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Article: Howling is a behavior commonly observed among a wolf nark. An animals, wolves work together to hunt and rely on howling was an important means of communication each other. There are different explants of a wolf's howl and it appears that there may be more to discover. One theory is that wolves howl to bend better together. It's almost as if howling together helps the pack stay together. Perhaps something similar to people feeling a sense of involvement with each other when singing a song together . But this theory may be wrong, explains Fred H. Harington, a professor who studies wolf behavior. Indeed, there have been tines when wolves have been seen one moment howling in a exhorts, and the next, quarreling anions each other. It appears that usually the lowest-tanking menthes of the pack may actually be "punished" for Joining in the churs at times. So is howling a way to strcagthen a social boad or just a way to reconfirm status among its members? ----Why do welves howl for sure? What is cleat, however, is that howling is often used among packmates to locate each other. Hunting grounds are distant and it happens that woloves may separate from one another at times. When this happens, howling appcars to be an ercellent means of gathering. Howling, interestingly, is a contagious behaviour. When one wolf starts to howl, very likely others will follow. This is often seen to occat in the morning, as if wolves were doing some sotr of "roll rall"where wolves all howl togeter to howl, very likely others will follow. This is often seen to occar in the morning, as if wolves were doing w some sotr of "roll call"where wolves all howl together to repotr their pteence.
Answer: The sense of belonging to a group.
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.What the por similarity between wolves' how humaes ting in chorus?

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Article: Global warming happens when greenhouse gases trap heat and light from the sun in the earth's atmosphere, which increases the temperature. This is like when heat is trapped in a car. On a hot day, the car gets hotter when it is out in the parking lot. This is because the heat and light from the sun can get into the car, by going through the windows,but it can't get back out. This is what the greenhouse effect does to the earth .The heat and light can get through the atmosphere, but it can't get out As a result,the temperature rises. Sometimes the temperature can change in a way that helps us. The greenhouse effect makes the earth appropriate for people to live on Without _ ,the earth would be freezing,or it would be burning hot. It would be freezing at night because we would not get the sun's heat and light .During the day, especially during the summer, it would be burning because the sun would be up with no atmosphere to filter it,so people,plants,and animals would be exposed to all the light and heat. Although the greenhouse effect makes the earth able to have people living on it,if there gets to be too many gases,the each can get unusually warmer, and many plants,animals.and people will die. Plants would die because they would not be able to take the heat .This would cause us to have less food to eat, and it would also limit the food that animals have. With less food for the animals that we need to survive we would even have less food. Gradually, people,plants,and animals would all die of hunger. People are doing many things to try to stop global warming .One thing is carpooling--driving with someone to a place that you are both going to. Another thing is being more careful about leaving electrical devices turned on. Now, more people are even riding buses or bikes to lower the amount of greenhouse gases in the air .Although adults do many things to help stop global warming, kids call do just as much.
Answer: It prevents all the light from the sun shining on the earth.
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What is the effect of atmosphere?

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Article: YOU probably think you know about London's problems. The people are unfriendly, it's way too expensive, and the food is terrible - so why do so many tourists flock there? London was named the world's most popular city between July and September 2013. It _ other world-famous cities such as New York and Paris, welcoming 4.9 million visitors, according to the UK Office for National Statistics. Amazingly, this was an increase of almost 19.5 percent on 2012 - the year when the Olympics happened in summer. So can London's success be explained? Well, maybe. As the English writer Samuel Johnson once said, "when a man is tired of London, he is tired of life". London life is often crazy and expensive, but if you can think of something, you can probably do it there. Anywhere in the city, you can often look around a great museum such as the British Museum, watch a concert at a historic venue like the Royal Albert Hall, or dance the night away in a cool nightclub such as Fabric. And it's not just about culture - there are also world-famous sporting venues around the city. Many tourists like to watch soccer matches at stadiums such as Chelsea's Stamford Bridge, Arsenal's Emirates Stadium, or Tottenham's White Hart Lane. Tourists even came to watch British tennis player Andy Murray's famous victory at the Wimbledon tennis tournament in 2013. Yes, but what about the food? Well, even if you don't like British food - and if you've never had real fish and chips, or a summer pudding, then perhaps you should wait until you've tried them - there is plenty of great food from all over the world available in London's many restaurants. London, like many of its buildings, has a long history, but also never lacks a vibrant pulse . All over the city, history and modernity come together to make it an essential place for tourists to discover.
Answer: To analyze why London appeals to tourists.
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What is the author's main purpose in writing the article?