You will be given a definition of a task first, then some input of the task.
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: A clinic in West Kalimantan, Indonesia, works to support the health of people and forests. Kinari Webb is an American doctor who helped start the non-profit group that operates the clinic. The group is known as ASRI. Dr. Webb says most communities value the local forests, but illegal logging was often their only way to earn money to pay for health care. "Villagers know that if they protect the forest, that's good for their long-term well-being. But if they have no money to see a doctor, they have to do illegal logging," said Dr. Webb. The clinic is in Sukadana, a village outside Gunung Palung National Park. Each month someone from ASRI visits the surrounding villages to see if they are actively logging or burning land within the park. Communities that do not take part in illegal logging pay about 40 percent less for health care than those that do. Also, the clinic uses a barter system. Patients can pay with things like handmade baskets, labor exchanges, young trees or fruit they grow. Patients learn about environmental conservation as they wait to register at the clinic. Many of the 70 staff members also help communities learn about organic farming and other ways to earn money. In May, ASRI started a program to identify forest "guardians". These guardians work with the community to try to prevent illegal logging. One of the guardians says he entered the program because ASRI helped his son recover from tuberculosis . The clinic is small, but very busy. However, people did not trust the clinic at first. They wanted to go to the only hospital in the area. Yet its resources are limited and villagers often have to travel more than two hours to get there. Now, people happily share stories about the clinic. Amelia's mother is one of them. She started going there when her daughter was eight months old. She says the treatment is good. Dr. Webb smiled when she heard that. Dr. Webb said: "Health care is an incredible key. And everyone everywhere around knows that we really care and that we are helping save their lives."
Question: A barter system is a system in which _ .
Options: (A) people trade by the exchange of goods (B) patients can receive a free treatment (C) customers pay the goods in cash (D) trees are taken good care of
Output:
A