A、It is just about any amount of physical activities that improve fitness. B、It is just anything that you need to exert yourself

M: Mrs. Ralph, we know that you have done some of the largest studies on exercise and health. Would you like to give us some tips on how to exercise and keep fit?
W: I would be glad to.
M: My friends are mostly young and healthy. They say they are doing fine without exercises. Is a regular workout really that important?
W: Sure it is. If one doesn’t exercise regularly, he’s missing out a lot. A person who is inactive may increase his chance of disease. For one thing, he may have sleep problems or easily catch a cold. And obesity is often the result of lack of exercise. So high blood pressure and heart problems may develop as he grows old. On the other hand, if one adds regular activities to his life, he is sure to benefit.
M: That sounds amazing. No wonder I will feel restless if I omit one or two sessions when I am too busy. But another question is, what types of exercise are there to keep fit?
W: Basically, there are four types of workouts that help us get in shape. The first type is cardio-vascular exercise. This exercise helps strengthen the heart by working it harder. Swimming, running, brisk walking, vigorous rowing, or just anything that you need to exert yourself to do to burn calories and make the heart beat faster.
M: Right. What about the second type?
W: The second type is endurance exercise. That trains the heart, lungs, and muscles to work hard for a longer time. Thus, while regular 20-minute walks may help you live longer, regular one-hour walks can help you play longer. The third type is strength training, which builds muscles. The improvement is little felt and fleeting at first, but regular use of the same muscles eventually increases their size and strength.
M: You mean like those body-builders who have got enormous and beautiful muscles?
W: Not exactly. Strength training isn’t just for the vain: having stronger back and abdominal muscles, for example, supports your spine, making back trouble less likely.
M: I see.
W: The fourth type is flexibility exercise, which keeps muscles long and supple, so they’re less likely to be injured.
M: Do we have to engage in all those forms of exercise in order to stay in shape?
W: Not necessarily. It all depends on your need, and also age. Younger people could engage in more vigorous activities or deliberate workouts, while the older people could just try anything that burns a little more calories, like walking or even gardening. The word "exercise" can be quite loosely defined. It can include out-of-the-gym activities, such as lawn-mowing, leaf-raking or even cleaning the house. Just about any amount of physical activity will improve fitness.
M: Then when should one begin?
W: One could get started at any time, any age.
1. According to the man, what attitude do most young people hold toward keeping healthy?
2. Which of the following is NOT a problem an inactive person may suffer from?
3. What does Mrs. Ralph take "brisk walking" as an example of?
4. Which of the following is CORRECT about muscle-building?
5. How is "exercise" defined in the conversation?