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.

Let me give you an example: Article: Homework can put you in a bad mood , and that might actually be a good thing. Researchers from the University of Plymouth in England doubted whether mood might affect the way kids learn. To find out the answer, they did two experiments with children. The first experiment tested 30 kids. Someshapes were hidden inside a different, larger picture. The kids had to find the small shapes while sitting in a room with either cheerful or sad music playing in the background. To test their mood, the scientists asked the kids to point to one of five faces, from happy to sad. Children who listened to cheerful music tended to point to the smiley faces while the others pointed to the unhappy ones. The researchers found that sad kids took at least a second less to find the small shapes. They also found an average of three or four more shapes. In the second experiment, 61 children watched one of two scenes from a film. One scene was happy, and the other was sad. Just like in the first experiment, kids who saw the sad scene acted better compared to the others. The researchers guessed that feeling down makes people more likely to focus on a problem or difficult situation. Not all scientists agree with them, however. Other studies argued that maybe, that cheerful music in the first experiment distracted kids from finding shapes. While scientists work on finding out the answers, it still might be wise to choose when to do your tasks according to your mood. After eating a delicious ice cream, for example, write an essay.
Question: Researchers did experiments on kids in order to find out _ .
Options: (A) how they really feel when they are learning (B) whether mood affects their learning ability (C) what methods are easy for kids to learn (D) the relationship between sadness and happiness
The answer to this example can be: B
Here is why: It is clearly mentioned in the article that to the check effect of mood on children is the main purpose of the experiment. So, B is the correct answer.

OK. solve this:
Article: Researchers in the US say they might have discovered how to fight against and even _ some processes of ageing, at least in mice. Injecting the blood of young mice into the older ones improved their brainpower, a study found. Scientists at Stanford University plan to carry out trials in people in the hope that new treatments for dementia can be developed. "There are factors present in blood from young mice that can recharge an old mouse's brain so that it functions more like a younger one,"says Dr. Tony from Stanford University School of medicine. In the study published in Nature Medicine, mice aged 18 months were given injections of the blood taken from mice aged 3 months. The injected mice performed better on memory tests than mice of the same age that had not been given the blood. Dr. Tony said it was not known whether the same was true of humans, but a trial was planned. A research center in UK said the treatment restored certain aspects of learning and memory in mice, but was of unknown importance to humans. The research, while very interesting, did not test the type of brain damage that was seen in dementia, which is not a necessary consequence of ageing. Meanwhile, two similar studies by a separate team have thrown more light on how young blood may benefit the old, in mice at least. A substance in the blood of mice previously shown to have an anti-ageing effect on heart muscle also improved brain cells, according to a Harvard team. The research, published in Science, found the blood factors encouraged the growth of brain cells in old mice, and restored their sense of smell. The same chemical also improved muscle power of aged mice, the researchers found.
Question: Scientists in the US will test the discovery in humans with the aim of _ .
Options: (A) proving the possibility to live longer. (B) showing the importance of scientific research. (C) publishing the study in Nature Medicine. (D) treating an age-related disease successfully.
Answer:
D