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.

Ex Input:
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

Ex Output:
D

Ex Input:
Article: These days, if you still think the cellphone is just for talking, you will get laughed at. Yes, it's true, voice-only handsets have become out of date. Today's do-it-all mobiles have a lot in common with the computer. The only difference may be that they fit in your pocket and you pay by the minutes to use them. Some of the things a cellphone can do for you will be available this year: Surf at speed Cellpones that let you use the Web have been around for years. So, what's new? Well, faster third-generation(3G) net works let you surf at anywhere. This then allows a carrier to send video, music, and games to your phone. Possible choices are from LG Electronic VX 8000 and Motorola V 1150. Listen as you go The problem with most cellphone MP3 players is that they hold only a handful of songs. But, that's about to change. Sony Ericsson's new W800i can hold around 150 songs in its 500 MB memory. And Sumsung's SPH-V5400 even comes with a 1.5 GB hard drive. Mobile phones may eventually replace mini-MP3 players, especially for teens. Say cheese Camera cellphones are not new either. But, most of them have limitations: around 1-megapixel . But new technology has made 2-megapixel units more common and 3-megapixel units are showing up soon. Some 2-megapixel models, like Sony Ericsson's K750i, offer limited zoom and focus controls. Others, like LG's recent MMA7110, can even capture 30 minutes of full- motion video. Portable TV You say you like "watching TV"? That's what Sumsung MM-A700 wants to give you. The new model lets users watch popular TV programs--for a fee. Other choices are Nokia's 6620, Sanyo's MM 7400 and NEC's N940.The NEC model lets you watch public TV--no fee. The above are just a handful of what you will see in the coming months. Further down the road, your mobile phone may play a host of other roles, such as mobile credit card, position locator... So what is there that a cellphone can't do?
Question: Which of the following models should you choose to listen to the music?
Options: (A) Sumsung's SPH-V5400 and Nokia's 6620 (B) Sony Ericsson's W800i and Sumsung's SPH-V5400 (C) Sony Ericsson's W800i and NEC's N940 (D) Sanyo's MM7400 and NEC's N940

Ex Output:
B

Ex Input:
Article: One of the best-known American writers of children's books is Alfred Strong, or Doctor Strong, as he is better known to readers everywhere. Now, an art show called "Doctor Strong From Then to Now" is travelling around the United States. The pictures and drawings show the history of Doctor Strong. Doctor Strong first became famous almost fifty years ago when his first children's book was published. Since then, he has written forty-five books that have sold more than one hundred million copies around the world. Doctor Strong's books are known for their easy use of words and colorful, hand-drawn pictures. These drawings bring life to his imaginary creatures. The Cat in the Hat, Horton the Elephant, The Grinch Who Stole Christmas, and hundreds of others. The San Diego Museum, in California, organized the art show. It included about three hundred Doctor Strong's original drawings and some of his writings. Most of Doctor Strong's books, although written in a funny way, have serious messages. For example, in Mc Elligot's Pool, he describes the danger of pollution. He discusses the arms race in The Butter Battle Book, written in nineteen eighty-four. Doctor Strong is almost eighty-four years old now. He says he never planned to write stories just for children. He says he writes stories that interest people of all ages. He says he uses easy words so that everyone, even a child, can understand.
Question: Alfred Strong is a famous _ in the United States.
Options: (A) doctor (B) artist (C) writer (D) reader

Ex Output:
C