A、Because they had caught serious disease. B、Because they had been away from home for many years. C、Because it was said they had

Marco Polo was an Italian man, born in 1254. He was a world traveler. When he was around 16 years old, he traveled with his father and his uncle a long way from Europe to China. After staying nearly twenty years in the East, they returned home at last. Their friends were surprised to see them again. They had been away for twenty-four years and everybody thought that they must have died a long time ago. But Marco Polo didn’t stay at home for long. He was taken as a prisoner in a sea battle. Time passed slowly in prison. Marco Polo was not in the least lonely. Every day he told the other prisoners about his travels. The stories he told of the countries of Asia were so interesting that one of the prisoners started to put them down in a book. In the book Marco Polo told about all the things he had seen and heard. He told of how the Chinese burned a kind of black stone for cooking, and how the heat it gave was much bigger and lasted much longer than a wood fire. People read it, but they said, "This book cannot be true." When he was an old man, he was ill and dying. Some of his friends came to see Marco Polo. Marco Polo said to them, "Everything in my book is true. I went to all those countries, and I saw all those strange things. It’s all true." So his friends believed him. Soon his stories got around and his name is remembered to this day.
Questions 19 to 21 are based on the passage you have just heard.
19. Why did the friends think that Marco Polo and his father must have died?
20. What kind of stories did Marco Polo tell the prisoners?
21. What did Marco Polo say to his friend before his death?