单项选择题

All over the world people swim for fun. Swimming is enjoyed by people-of (41) ages (年龄), from the very young to the very old. There are many places (42) people to swim. Some people swim in lakes, rivers and seas, (43) swim in swimming pools. Many schools, hotels and clubs (俱乐部) have swimming pools. Some people have pools of (44) in their yards (院子).
Swimming is one of (45) forms (形式) of exercise. It can make hearts and bodies (46) . It can also help blood circulate (循环). Handicapped (残疾的) people can (47) their bodies in better condition (状况) by swimming (48) they can’t enjoy other sports. (49) is a good idea for us to learn to swim at an early age. (50) we will enjoy it for the rest of our lives.