阅读下面材料，从每题所给的四个选项（ABCD）中选出最佳选项。
B
We all need to exercise. Doctors say it is good for us. It makes our heart and body strong. It also gives you more energy(能量). And you will feel better about yourself. It's best to exercise twice a week. Twenty minutes each time is enough.
There are many ways to exercise. You can walk, run, play sports or swim. Many people go to special places to exercise. They are called "fitness centers". These places have a lot of equipment(设备). Some people buy equipment for their homes. But it's very expensive.
Exercising can be fun. Friends can exercise together at fitness centers. Or they can play sports together. How do you exercise? How often do you exercise?
