We have known for a long time that flowers of different plants open and close at different time of day. Yet no one really understands why flowers open and close like this at special times. It is not as simple as we might think, as new experiments(实验) have shown. In one experiment, flowers were kept in darkness. We might expect that the flowers, without any information about the time of the day, did not open as they usually do. In fact, they continued to open at their usual time. This shows that they have some mysterious (神秘的) way of knowing the time.

    Their sense of time does not depend on information from the outside world; it is, so to speak, inside them, a kind of “inner clock”. This discovery may not seem to be very important. However, it was later found that not just plants but also animals including man have this “inner clock”which controls(控制) working of their bodies and their activities.

    Human beings, then, are also controlled by this mysterious power. Whether we wish it or not, it affects such things in our life as our need for sleep, our need for food. And our ability to concentrate(集中).

    This is a street crossing. There are red and green lights at each corner. Drivers must watch the lights carefully.

    When there is a green light, the cars may go on. When there is a red light, the cars must stop.

    They must wait until the red light changes (变成)to green. Then they can go on. Sometimes the cars want to make a right turn or a left turn. They can make a right turn when the light is green or red. But they must wait until the green light is shining (闪亮) if they want to turn left. Some people are color-blind (色盲的). They can't see the difference (不同点) between red and green. These people mustn't drive, or there may be an accident (事故) .We must keep our street safe (安全的).

When Helen Keller was nineteen months old, a brief illness made her both deaf and blind. With such limitations, how could Keller ever be expected to find happiness?

Because happiness has been considered a personal concept, it is difficult to define（定义）. Many people throughout history have tried. Greek scientist and philosopher Aristotle wrote, "Happiness depends upon ourselves," which is not a definition but an observation that individuals are responsible for their own happiness. Roman statesman and philosopher Lucius Seneca wrote of a particular quality of happiness, saying, "True happiness is to enjoy the present, without anxious dependence upon the future."

Is there a scientific basis（基础）for happiness? Researcher suggests happiness is a matter of perspective: "Truly happy individuals construe life events and daily situations in ways that seem to maintain their happiness, while unhappy individuals construe（理解）experiences in ways that seem to reinforce unhappiness". Basically, this means the way you choose to remember events and situations affects your happiness.

Some research concludes happiness is made up of three parts: pleasure, engagement and meaning. Pleasure involves things that give physical and emotional joy, such as playing a sport or seeing beautiful art. Engagement involves positive interactions（互动）with other people, such as studying or working with people whose company you enjoy. Meaning relates to feeling that your work is useful and important to others.

Even with scientific rationalization（合理化）, questions remain. For example, are younger people happier than older people? In fact, the opposite seems to be true. This may be because younger people tend to experience higher levels of negative emotions, such as anxiety and anger. The young also have less control over their lives because they lack both independence and the ability to make many of their own decisions.

Perhaps the most important question is whether you can change how happy you are. Studies of identical twins suggest that genetics forms about half of your happiness level. Your quality of life influences about 10 percent of your happiness. That means about 40 percent of your happiness is determined by your choices and actions.

From this explanation we can see that one way you can make yourself happier is to set goals. Keller had a definition of happiness in keeping with this idea. She felt happiness did not come from simply trying to satisfy your own desires but rather by contributing your time and skills to improve the world in some way.

Even if you are unable to achieve a goal that makes the world better in some small way, simply trying will likely give your life meaning and, at the same time, happiness.

Franz Kafka was a famous writer. He never married and had no children. Once, at the age of 40, when Kafka was walking through a park, he saw a young girl crying. She lost her favourite doll. 

He helped her look for the doll, but they couldn't find it. Kafka told her to meet him there the next day and they would look for it again. 

The next day, when they still didn't find the doll, Kafka gave the girl letter" written" by the doll that said, " Please don't cry. I have gone on a trip to see the world. I'm going to write to you about my adventures. "

Thus(由此) a story that continued to the end of Kafka's life began. 

When they met every time, Kafka read aloud the letters( which he had written, of course) of adventures that the girl found exciting. Finally, Kafka read her a letter in which the doll said it had finally returned to Berlin. Then, he gave her a doll that he had bought. 

" This does not look like my doll at all, " she said. Kafka handed her another letter that said, " It is my trips that have changed me. " The girl took the doll home happily. A year later, Kafka died. 

Many years later, the girl found a letter hidden inside the doll. It said, " Everything you love is very likely to be lost, but in the end, love will return in a different way. "

Cindy brought home a notice from school: 

School Uniform Rules

Sept. 9th, 2018

Dear parents, 

Some parents have asked about the rules about dress at Popular School. Please read and buy the right uniforms for your children this winter. 

Children can be allowed to wear blue scarves or white scarves to school. But they aren't allowed to wear hats. 

The school uniform must be clean. Girls with long hair must tie（扎）their hair with yellow ribbons（丝带）. 

Children can only wear sports shoes to school if they have a PE lesson that day. They are allowed to wear white sports shoes only. 

Thank you for your attention. 

Sincerely, 

John Wong （Head teacher）

 Cats and dogs are some of the most popular pets. There is an old question-which one is better and why?

 If you ask me, I'm a cat person through and through. To me, there is nothing better than having a cat of your own. Every time I see a cat, I am filled with so much joy! Don't even get me started on all of the cute cat videos online. 

 Cats are very independent animals. They like to have their personal space. But this doesn't mean that they don't love their humans(人类). Cats may seem standoffish(冷淡的) at first, but they can quickly warm up to their owners and become their very best friends. 

 Cats can also be a lot of responsibility (责任) and hard work. For example, cats like to be clean. You usually don't need to give them baths, but you do need to keep their fur clean and clean their litter boxes every day. Not only this,    ▲    . Cats don't need to go outside for daily walks like dogs do, but it's important to give them a lot of exercise through playtime. 

 For me, cats are the perfect friends. There's nothing better than a cat sitting next to you after a long day of work. So why not choose cats as your pets?