Choose the correct letter, A, B or C. Which benefit of exercise does Debbie think is most important?

Good afternoon. My name’s Debbie Green and I’m going to give you a short but hopefully interesting introduction to working at this hospital. I’ll start with some guidelines about nutrition and fitness... er, because a hospital environment can be stressful, and so we always encourage our staff to stay fit and have a healthy lifestyle. So... just a few tips first. As you know, the key to good health is eating what we call ’a balanced diet’; many people don’t do this, however. For one thing, they don’t eat enough fruit and vegetables or home-prepared food. When you feel hungry, it’s often too easy to grab something quick, because you’re tired or busy. Cooking a healthy meal takes longer, and this is often why people live on sandwiches and fast food instead. Please don’t fall into this unhealthy trap.
Of course, you have to do a little exercise and keep fit as well. I know you’ll have a lot of work and may not have time to join a gym... but consider how often you take the lift, rather than the stairs, or how often you drive rather than walk. Health wise, it may just be a question of doing things differently, rather than starting a very active sport.
In fact, being generally active is much healthier than doing lots of exercise just occasionally. As you know, this can be as risky for your heart as being inactive! As long as you do at least an hour’s exercise a day — and some of you will do more than that at work — you’ll find that you don’t lie awake at night worrying about the next day — and that’s the main advantage of exercise. Remember — this is a hospital, and you are supposed to be the healthiest people here!
Moving on to health and safety, I want to point out that it’s quite OK to take a break any time that you’re not busy. We know that when there’s an emergency you may have to miss that cup of tea or coffee in the canteen or wherever you go, but generally you shouldn’t work for more than three hours without a break, otherwise your attention levels will drop and you could then make a careless mistake.
Another important issue is hygiene. You’re all trained to clean your hands at work, but remember that germs can live for a long time, so please make sure that you don’t leave even a small amount of rubbish around... there are brooms in the cupboards, so use them. We do have cleaners, but they aren’t always here when you need them, I’m afraid, and a little dirt can soon build up.