Dolphins are not fish; they’re mammals. They are warm-blooded like man and give birth to one baby called a calf at a time. At birth a calf is about 90—130cm long and grows to about 4m. They live up to 40 years. They are highly sociable animals.

Their teeth are interlocking rows of hooks, suitable for holding slippery fish. They eat fish whole starting with head first. When they go wild they keep their mouth open and sometimes keep it nodding to express their aggression. Greater aggression is shown by violent jaw clapping. Dolphins breathe through their blowhole(呼吸孔) located at the top of their head. The dolphin’s eyes produce a special slippery secretion(分泌物) which protects the eyes from foreign objects and water friction.

Dolphins use their powerful tail to move through the water. They also use their tail while hunting. They slap their tail rapidly when they get annoyed or when they want to indicate the sign of danger to alert other dolphins.

The dolphin’s skin is completely smooth allowing the dolphin to move easily through the water, and also reduce heat loss. Their skin may bear rake marks from other dolphin’s teeth during play or mating, and can easily become badly sunburned if they strand(搁浅).

Their bodies are very streamlined so they may swim at high speed through the water, and an example of this is their ears. Dolphin’s ears are barely noticeable marked only by a small hole just behind the eyes.

While sleeping, it shuts down only half of its brain, as its breathing is under voluntary control. Dolphins take short catnaps, floating just below the surface, and then slowly rising to breathe. Often dolphins are very active during night time, for some this is their main feeding time. Dolphins are able to dive to great depths, and also leap to great heights. They may leap to avoid predators or to show how powerful they are to females at mating time.

How often do you exercise? A new study found that most kids aged 12 to 15 weren’t getting enough physical activity. The results were based on about 800 kids. As part of the study, the kids reported on their own activity levels, and took physical exams. According to the study, only 25% of U.S. kids get enough physical activity.

“It's certainly worrying to see that our kids have such a limited amount of physical activity each day,” said Dr. Stephen Pont. He is an expert on children's health.

Few kids in the study met the requirement on physical activity that raises the heart rate and makes people breathe harder. Overall, about 25% said they got an hour of that kind of exercise every day. Kids also reported on which activities they did most often outside of school gym class—basketball for boys and running for girls.

“There's always room for improvement,” said Tala Fakhouri, who was the leader of the study. Fakhouri visits schools and holds exercise events. She also calls on schools to offer regular gym classes.

The study also found kids who get physical education at school may get better grades in study.

One way to prevent anxiety from getting out of control is to recognize its benefits. It is a mistake to think that we can make better decisions if we keep our feelings under control.Instead,a mix of feelings like anxiety and logical thinking leads to sound decision-making. There is plenty of research showing that higher levels of anxiety can make us more likely to avoid risks in our decision-making.There is also evidence that anxiety can increase the attention you pay to relevant information.

Recent studies have shown that people who are anxious about their relationships (for example,they fear to be abandoned) tend to be better at recognizing people who tell lies and are more likely to raise the alarm when danger approaches.

In the real world though, it’s worth realizing that feeling anxious for a while is very common.It helps you communicate with others that you care about, and what’s more, it’s probably a sign that you are intelligent. At least two published studies have identified that people who score higher on measures of anxiety also tend to perform better on intelligence tests. This seems reasonable: If you’re a thinker, you are sure to be always thinking about the future and imagining possible plots, including bad ones.

The important thing, if you are a person likely to worry, is not to let your fear destroy your dreams. And don’t bury your head in the sand. Instead, act on your fears - do research as well as preparation.So rather than walk blindly into what you fear, why not meet challenges in full readiness?

When anxiety beats you, or casts a shadow over your life, this is a serious problem.No one is denying that. But like everyday anxiety of this kind that you feel before a presentation or interview,you needn’t see it as your enemy. Anxiety is an important feeling，developed through evolution(进化).As for people who are fairly anxious by nature, there is a reason to cheer,too.Your nerves are a sign of your watchfulness. Listen to them and act on them. Then you can turn your nervousness into your advantage.