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: Trees are useful to man in three important ways: They provide him with wood and other products; they provide him shade;. and they help to prevent droughts and floods. Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important.In his eagerness to make money from trees, he has cut them down in large numbers, only to find that without them he has lost the best friends he had. And besides, he is usually too careless to plant and look after new trees. So the forests slowly disappear. This does not only mean that man will have fewer trees. The results are even more serious: for where there are trees, their roots break up soil allowing the rain to sink in and also bind the soil, thus preventing it from being washed away easily;but where there are no trees, the rain falls on hard ground and flows away, causing floods and carrying away the rich top-soil. When the top-soil is gone, nothing remains but worthless desert. Two thousand years ago,a rich and powerful country cut down its trees to build warships, with which to gain itself an empire .It set up the empire, but, without its trees, its soil became poor and grew weak. When the empire fell to pieces, the home country found itself faced by floods and starvation .
Question: The most important service of trees to man is that _ .
Options: (A) they give them wood and other products (B) they give them shade (C) they help him prevent droughts and floods (D) they help him made money

Ex Output:
C

Ex Input:
Article: Many songs, poems, and books have been written on love's strong effect on people. The state of being in love has even been compared to being sick or mad. A study by Professor Semir Zeki of University College London has found that love does affect people's brains by making them feel great. Zeki studied young men and women who had recently fallen in love. He found that, when they were looking at photos of their loved ones, there was heightened activity in four areas of their brains. These areas deal with emotions, and one of them, in particular, is known to respond to drugs that cause feelings of great joy and excitement. Interestingly, the study also found a lack of activity in two other areas of the brain when the volunteers looked at their lovers' photographs. One of these areas is linked to feelings of sadness, while the other is often active in people suffering from depression. It seems love really can be _ . The state of being in love, according to some scientists, may actually be good for your health. Although scientists know that being in love can make a person feel great, the exact influence of love on a person's health is harder to determine. However, scientists say that people do need love in order to live healthy lives. According to Dr. Thomas Lewis, people need to be in relationships because that is how we are designed. He says the brain can only maintain the overall stability of a person's immune system, bodily rhythms, and heart if it receives input from outside the body in the form of emotional connections with others. Professor Antonio Damasio has a similar view. He says that love enriches a person's imagination and creativity, and makes a person's body work better. He also believes that love can even improve the body's ability to fight against disease. Damasio's wise words of advice are " Choose love and you will live longer."
Question: The main idea of this passage is _ .
Options: (A) love can really cause people active (B) love has effect on songs and books (C) love is linked with emotion (D) love is what we need

Ex Output:
D