"An apple a day keeps the doctor away." Well, milk may work in the same way! Milk is the natural food for mammalian  babies. It helps them grow strong because it is rich in protein , calcium  and vitamins. Milk can also help you sleep better because it calms you down. But remember to drink milk with care. Find out how old the milk is. Make sure it is fresh and hasn't gone bad. Don't drink milk when your stomach is empty. Eat some bread or corn at the same time. That'll help you take in more protein and vitamins. Doctors say teens need at least 500ml of milk a day. That's two or three cups. Milk-drinking started long ago, as early as 6,000-8,000BC. At that time people started to keep cows, sheep and goats to get their milk. Of course what you drink today isn't that fresh from the cow. People cool the fresh milk down to 40C to stop the bacteria growing. In factories, milk is pasteurized  to stop it growing bad. After disinfections  and packaging, it goes to the supermarkets. Yoghourt also comes from milk. People make some special bacteria to change the taste of milk and make the nutrients  in it easier for people to take in. Maybe that's why it's getting more popular with people! The sentence "An apple a day keeps the doctor away." tells us that  _  .
the doctor likes to eat apples every day the doctor doesn't like apples at all the doctor eats an apple each day apples are good for our health