A、A glass of milk. B、Nothing. C、A meal. D、Kindness. B

One day, a poor boy who was trying to pay his way through school by selling goods door to door found that he only had one dime left. He was hungry, so he decided to beg for a meal at the next house.
    However, he lost his nerve when a lovely young woman opened the door. Instead of a meal he asked for a drink of water. She thought he looked hungry so she brought him a large glass of milk. He drank it slowly, and then asked, "How much do I owe you?"
    "You don’t owe me anything," she replied. "Mother has taught me never to accept pay for a kindness." He said, "Then I thank you from the bottom of my heart." As he left that house, he not only felt stronger physically, but also increased his faith in God and the human race.
    Years later the young woman became critically ill. The local doctors were baffled. They finally sent her to the big city, where specialists could be called in to study her rare disease. Dr. Howard Kelly, the poor boy, now famous, was called in for the consultation. When he heard the name of the town she came from, a strange light filled his eyes. Immediately, he rose and went down through the hospital hall into her room. He recognized her at once. He went back to the consultation room and determined to do his best to save her life. From that day on, he gave special attention to her case.
    After a long struggle, the battle was won. Dr. Kelly requested the business office to pass the final bill to him for approval. He looked at it and then wrote something on the side. The bill was sent to her room. She was afraid to open it because she was positive that it would take the rest of her life to pay it off. Finally she looked, and the note on the side of the bill caught her attention. She read these words, "Paid in full with a glass of milk."