Once a group of 17-year-old schoolboys decided to break the world basketball marathon record . They wanted to play for ninety hours and that is to add six hours to the record. Each team had nine players, with five at a time. The boys decided each person would play 21. 5 hours and then rest for 2 hours. Then they started at 6 o'clock in the evening. The first night was very hard for the players. When it was their turn to rest, they were too excited  to fall asleep at once. After sleeping for a short time, they had to play again. On the second night, they fell asleep as soon as they stopped. Some of them had trouble with their feet and hands, but the only serious problem was a psychological  one. Each boy was thinking:why am I doing this?How can I play any longer?After the third night, the players knew they could finish the ninety hours. The basketball on the fourth night was very slow. But in the final hours, the players got better. For the last few minutes, the players looked as fresh as when they started. How happy everyone was! In the story, there were   _   schoolboys playing basketball marathon.
9 14 17 18