Sports and games make our bodies strong, prevent us from getting too fat, and keep us healthy. But there are not their only use. They give us valuable practice in making eyes, brain and muscles work together. In tennis, our eyes see the ball coming, judge its speed and direction and pass this information on to the brain. The brain then has to decide what to do, and to send its orders to the muscles of the arms, legs, and so on, so that the ball is met and hit back where it ought to go. All this must happen with very great speed, and only those who have had a lot of practice at tennis can carry out this complicated chain of events successfully. For those who work with their brains most of the day, the practice of such skills is especially useful. Sports and games are also very useful for character-training. In their lessons at school, boys and girls may learn about such virtues as unselfishness, courage, discipline and love of one's country but what is learned in books cannot have the same deep effect on a child's character as what is learned by experience. The ordinary day-school cannot give much practical training in living, because most of the pupils' time is spent in classes, studying lessons. So it is what the pupils do in their spare time that really prepares them to take their place in society as citizens when they grow up. If each of them learns to work for his team and not for himself on the football field, he will later find it natural to work for the good of his country instead of only for his own benefit. When we play tennis we have to ______.