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.

Article: Supply and demand is perhaps one of the most basic concepts of economics and it is the backbone of a market economy. Demand refers to how much of a product or service is desired by buyers. The quantity demanded is the amount of a product people are willing to buy at a certain price; the relationship between price and quantity demanded is known as the demand relationship. Supply represents how much the market can offer. The quantity supplied refers to the amount of a certain goods producers are willing to supply when receiving a certain price. The relationship between price and how much of a goods or service is supplied to the market is known as the supply relationship. Price, therefore, is a reflection of supply and demand. The law of demand states that, if all other factors remain equal, the higher the price of a product, the fewer people will demand that product. The amount of goods that buyers purchase at a higher price is less as the price of a product goes up, so does the opportunity cost of buying that product. Like the law of demand, the law of supply shows the quantities that will be sold at a certain price. But unlike the law of demand, the supply relationship shows an upward slope. This means that the higher the price, the higher the quantity supplied. Producers supply more at a higher price because selling a higher quantity at a higher price increases the whole income. Now that we know the laws of supply and demand, let's turn to an example to show how supply and demand affect price. Imagine that a CD of your favorite band is sold for $20. Because the record company's previous analysis showed that consumers will not demand CDs at a price higher than $20, only ten CDs were sold because the opportunity cost is too high for suppliers to produce more. If, however, the ten CDs are demanded by 20 people, the price will then rise. As a result, the rise in price should cause more CDs to be supplied as the supply relationship shows that the higher the price, the higher the quantity supplied. If, however, there are 30 CDs produced and demand is still at 20, the price will not be pushed up because the supply is more than the demand.
Question: We know from the passage that changes in the prices of product cause changes in _ .
Options: (A) income and expense (B) invention and production (C) market and society (D) supply and demand
D

Article: Every culture has a recognized point when a child becomes an adult, when rules must be followed and tests passed. In China, although teenagers can get their ID cards at 16, many only see themselves as an adult when they are 18. In the US, where everyone drives, the main step to the freedom of adult life is learning to drive. At 16, American teens take their driving test. When they have their license, they drive into the grown-up world. "Nobody wants to ride the cheese bus to school," said Eleanor Fulham, 17. She brought the pressure back to memory, especially from kids from wealthier families. "It's like you're not cool if you don't have a car," she said. According to recent research, 41% of 16 to 19-year-olds in the US own cars, up from 23% in 1985. Although, most of these cars are bought by parents, some teens get part-time jobs to help pay. Not all families can afford cars for their children. In cities with subways and limited parking, some teenagers don't want them. But in rich suburban areas without subways, and where bicycles are more for fun than transportation, it is strange for a teenager not to have a car. But police say 16-year-olds have almost three times more accidents than 18 and 19-year-olds. This has made many parents pause before letting their kids drive. Julie Sussman, of Virginia, decided that her son Chad, 15, will wait until he is 17 to apply for his learner's permit. Chad said he has accepted his parents' decision, although it has caused some teasing from his friends. "They say that I am unlucky," he said, "But I'd rather be alive than driving, and I don't really trust my friends on the road, either." In China, as more families get cars, more 18-year-olds learn to drive. Will this become a big step to becoming an adult?
Question: Which may serve as the BEST title of the article?
Options: (A) Cars Helping You to Grow-Up (B) Driving into the Grown-Up World (C) Teenagers' Driving in America (D) Recognized Point of Becoming an Adult
B

Article: Sometimes I really doubt whether there is love between my parents. Every day they are very busy trying to make money for my schooling. One day, my mother was sewing a quilt . I silently sat beside her. "Mum, is there love between you and Dad?" I asked in a very low voice. With surprise in her eyes, she stopped her work for a while. Then she said, "Susan, look at this thread . It can hardly be seen, but it' s really there. It makes the quilt strong. If life is a quilt, love should be a thread. Love is inside. " I couldn' t understand her until the next spring. At that time, my father suddenly got sick seriously. My mother had to stay with him in the hospital for a month. After they were back, my mother helped my father walk slowly on the country road every day. They were so kind to each other and it seemed they were the happiest couple. After two months my father still couldn' t walk by himself. "Dad, how are you feeling now?" I asked him one day. "Susan, don' t worry about me," he said. "I just like walking with your mum. I like this kind of life." Reading his eyes, I knew he loves my mother deeply. Now I understand that love is just a thread in the quilt of our life. Love is inside, making life strong and warm.
Question: Susan's father stayed in hospital for _ .
Options: (A) one day (B) one month (C) two months (D) three months
B