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.

Input: Consider Input: 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

Output: B

Input: Consider Input: Article: The red crab lives on Christmas Island in the Indian Ocean and has been found nowhere else in the world. But on its homeland it is a very significant species -- some 120 million individuals cover the rain forest floor and play a major role in determining the structure of the ecosystem. These large crabs are active during the day but prefer to stay in the shade and can die in the heat of direct sunlight. They feed on fallen leaves, seeds, fruits and flowers, recycling nutrients and helping to determine the spread and composition of native plants. Most of the year the red crabs live in the holes they dig throughout the forest. During the dry season they hide in these shelters to keep their body wet and remain there for two to three months. But when wet season returns in October or November they begin a legendary mass migration to their seaside breeding grounds, moving in color1ful wave that wash over all obstacles like roads (including special passages and some closed roads built for the red crab) and even seaside cliffs. The annual migration is also closely tied to the lunar schedule. The crabs arrive at the coast and breed at such a time that the females can produce eggs and develop them in caves for a dozen or so days before carrying them into the sea exactly when high tide turns between the last quarter and new moon. During this period sea level on the beaches varies the least and offers an easier approach, which is so important that if the weather delays the migration crabs will put off laying eggs until the next lunar month. Red crab eggs grow right away, and the young live in the sea for a month before returning to the coast, changing into air breathers, and slowly returning inland to begin the cycle once again.
Question: The red crab is a very significant species on its homeland because _ .
Options: (A) it's gradually dying out (B) it's not found anywhere else (C) it's well protected by the local people (D) its huge population affects its native ecosystem

Output: D

Input: Consider Input: Article: Around three forty-five on a rainy Saturday morning, I was woken up by the sound of my pager beeping. As a volunteer firefighter and emergency medical technician, I can never count on a full night of sleep. I pulled myself out of bed and went toward the desk to grab my radio. Our crew was being sent to a nearby home where a man was in cardiac arrest . We found the man lying on the kitchen floor with his wife beside him. We rushed the patient to the hospital, but despite our efforts, we were unable to save his life. In my line of life, I rarely get any recognition from the patients we treat, or from their loved ones. But that night, a man's wife approached us, and through her tears, whispered, "Thank you." Then she hugged each of us. She knew we answered her late-night call for help, even though the ending was not positive. There is something deeply rewarding about helping people in these circumstances. Sometimes, I'm able to make their worst day a bit better: like seeing the tears of an injured child turn into a smile when I gave him an interesting toy; or watching a terrified mother's screams turn into tears of joy when she realized her baby was going to be fine. Experiences like these allow me to see the impact my work has on others. At the same time, I also know the effect _ has had on my own life. As a teenager, I felt awkward when my dad hugged me and said, " I love you, my dear son." I was equally uncomfortable and responded, "I love you." But then I imagined him lying on the kitchen floor that rainy night and realized that my opportunity to say those three words could---at any moment---be taken away forever. Now, I extremely treasure the moment when my father says those three words to me. I've learned to appreciate every relationship I have, to tell people I care about them, and to never take anything in life for granted.
Question: On that rainy Saturday morning, the author was woken to _ .
Options: (A) meet his father for the last time (B) put out a really big fire (C) save a man's life (D) do a scientific experiment
Output: C