Why are dogs our best friends? Maybe because they can understand our words much better than we think, according to a study in Hungary. The study shows that dogs understand not only what we say, but also how we say it. “The results are very exciting and surprising,”says Attila Andics, the lead researcher from a University in Budapest.

For the study, the researchers first trained 13 dogs for months. The dogs had to sit quietly inside machines so that the researchers could check their brain activity. Then the researchers put headphones on dogs and played people's voices to them. There were four different voices. Some were positive words, such as“well done”. Some were negative words like “not good”. The words were also in different tones(音调). Some were positive, some were neutral(中立的), and some were negative.

Brain scans(扫描) showed the dogs could recognize words, as well as the tone of words, much like people do. The positive words with a positive tone brought the strongest activity in their brains' reward centers (反应中枢).“It shows that for dogs, a nice phrase can work very well as a reward, but it works best if both words and tones match,”said Andics.

They also found that dogs deal with meaningful words with the left side of the brain and tones with the right. People's brains work in the same way.

Andics said it gave us a new understanding of the language. That is to say, not only humans understand the meaning in words, but also other species(物种) do too.

Water plays an important role in keeping you healthy. This should come as no surprise. Much of your body is made up of water, after all. It keeps your body working properly. But did you know that too much water can make you die?

Water poisoning (中毒) happens when people drink too much water. This lowers the level of sodium (钠) in their blood to dangerous levels. When you have too little sodium in your body, a lot of things will go seriously wrong in your body.

Your brain may begin to swell (膨胀). You may get a headache, feel very tired and sick. You may even lose consciousness. In these cases, water poisoning can be deadly. You will need to go to a hospital immediately.

Protecting yourself from water poisoning may seem easy, however, this is easier said than done. For example, when you do exercise, you may have to drink a lot of water. It is important to balance the amount (量) of water. This can help you stay healthy whenever you are exercising.

So, how much water should a person drink each day? For years, we have been told to drink two liters (公升) of water a day. But in fact, the actual amount needed is different for each person. Today, most doctors are telling people that they should drink water whenever they feel thirsty.

We can’t live without water. Neither can we live with too much water in our bodies.

Make sure you take the right amount of it each day—staying healthy is all about staying balanced.

Long, long ago there was no zero. To write the number sixty-three people wrote 63. To write six hundred and three, people wrote 63. The space between six and three was there to mean “not any” tens. Sometimes people did not remember the space. It was hard to see and read. Later people used a dot to hold the space. Six hundred and three looked like this 6.3. But the dot (点) was hard to see. So people put a circle around it like this 6⊙3.Then people could see the dot. They remembered the space. At last, only the circle around the dot was used. It was like a zero. This is one story of how the zero came to be used. Now zero has many important uses. Zero tells how many. Can you tell some other ways of using zero?