instruction:
In this task, you're given an article, a question which often contains a blank and four options (associated with "A", "B", "C", "D"). Your task is to find the correct answer (from the given options) for the question from the given article and return one of the options from "A", "B", "C", and "D". Do not generate anything else apart from one of the following characters: "A", "B", "C", "D". There is only one correct answer for each question.
question:
Article: Winter begins in the north on December 22nd. People and animals have been doing what they always do to prepare for the colder months. Squirrels , for example, have been busy gathering nuts from trees. Well, scientists have been busy gathering information about what the squirrels do with the food they collect. They examined differences between red squirrels and gray squirrels in the American state of Indiana. The scientists wanted to know how these differences could affect the growth of black walnut trees. The black walnut is the nut of choice for both kinds of squirrels. The black walnut tree is also a central part of some hardwood forests. Rob Swihart of Purdue University did the study with Jake Goheen, a former Purdue student now at the University of New Mexico. The two researchers estimate that several times as many walnuts grow when gathered by gray squirrels as compared to red squirrels. Gray squirrels and red squirrels do not store nuts and seeds in the same way. Gray squirrels bury nuts one at a time in a number of places. But they seldom remember where they buried every nut. So some nuts remain in the ground. Conditions are right for them to develop and grow the following spring. Red squirrels, however, store large groups of nuts above ground. Professor Swihart calls " _ ". Gray squirrels are native to Indiana. But Professor Swihart says their numbers began to decrease as more forests were cut for agriculture. Red squirrels began to spread through the state during the past century. The researchers say red squirrels are native to forests that stay green all year, unlike walnut trees. They say the cleaning of forest land for agriculture has helped red squirrels invade Indiana. Jake Goheen calls them a sign of an environmental problem more than a cause.
Question: The study done by Rob Swihart and Jake Goheen is to _ .
Options: (A) find out the living conditions for squirrels (B) learn squirrels' influence on black walnut trees (C) do something to get rid of squirrels (D) save the forests in the American state of Indiana
answer:
B

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Article: Humans and many other mammals have unusually efficient internal temperature regulating systems that automatically maintain stable core body temperatures in cold winters and warm summers. In addition, people have developed cultural patterns and technologies that help them adjust to extremes of temperature and humidity . In very cold climates, there is a constant danger of developing hypothermia , which is a life threatening drop in core body temperature to below normal levels. The normal temperature for humans is about 37.0degC. However, differences in persons and even the time of day can cause it to be as much as 6degC higher or lower in healthy individuals. It is also normal for core body temperature to be lower in elderly people. Hypothermia begins to occur when the core body temperature drops to 34.4degC. Below 29.4degC, the body cools more rapidly because its natural temperature regulating system usually fails. The rapid decline in core body temperature is likely to result in death. However, there have been rare cases in which people have been saved after their temperatures had dropped to 13.9-15.6degC. This happened in 1999 to a Swedish woman who was trapped under an ice sheet in freezing water for 80 minutes. She was found unconscious, not breathing, and her heart had stopped beating, yet she was eventually saved despite the fact that her temperature had dropped to 13.7degC. In extremely hot climates or as a result of uncontrollable infections, core body temperatures can rise to equally dangerous levels. This is hyperthermia. Life threatening hyperthermia typically starts in humans when their temperatures rise to 40.6-41.7degC. Only a few days at this extraordinarily high temperature level is likely to result in the worsening of internal organs and death.
Question: Why can humans keep stable body temperatures in different seasons?
Options: (A) Because their bodies are unusually efficient. (B) Because they experience different climates. (C) Because they can adjust to cultural patterns and technologies. (D) Because they have internal temperature regulating systems.
answer:
D

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Article: Scientists warn today that the Atlantic bluefin tuna faces disappearance unless certain action is taken. They used electronic ways to track the movement of the powerful fish from the Gulf of Mexico to the Mediterranean, and report today in the journal Nature that meals of sushi and sandwiches with tuna worldwide are more dangerous than anyone has imagined. The bluefin tuna can live for 30 years, grow to three metres in length and weigh as much as 700kg. A good one can fetch as much as PS 52,000 in the Tokyo fish markets. "In my lifetime, we've brought this big fish to the doorstep of death in the western Atlantic Ocean," said Barbara Block of Stanford University in California. "The electronic way of tracks provides the best scientific information we've ever had to manage these tuna and we must, as an international community, start to act actively to make sure of the future of this fish. " Scientists have repeatedly said that the harvest of the seas cannot be as good as before. There are fewer and fewer fish in around Newfoundland, North Sea and Iceland, so fishermen have pushed further offshore in search of deep ocean fish. Tuna--in the Mediterranean and Japan--have been under increasing pressure for years. The International Commission on the Conservation of Atlantic Tuna has tried to manage the fish since 1969.There are two populations: a western one that has dropped by 80% in the past 30 years, and a larger, eastern population. Although catches are controlled by 3,000 tons a year in the western fishery, and 32,000 in the east, no one knew whether the limits worked. So Professor Block and her team placed tracks on hundreds of the fish and tracked them to depths of more than 900 metres and on journeys of thousands of miles, measuring the movement, body and water temperatures. "There are two ways to save the Atlantic bluefin tuna--protect them in their production grounds and in their feeding grounds," Prof. Block said. "This will need immediate action in both the central Atlantic, to reduce the loss of the big fish while hunting, and in the Gulf of Mexico and Mediterranean, where tuna produce as separate populations. "
Question: The bluefin tuna in this passage mainly refers to the one _ .
Options: (A) in the Atlantic (B) in the Pacific (C) in the Gulf of Mexico (D) in the Mediterranean
answer:
A