"Listen carefully to what I say," the time traveler said, "I shall tell you something that you will not agree."  

 "Why will we not agree?" I asked.

 "Because the science and mathematics you know are not correct,"  he said. "You believe there are only three dimensions(三维空间)-length, breadth(宽) and thickness." 

 "There is nothing to argue with that, " the youngest member of our little group said.

 "Exactly!"  the time traveler answered, "But there is also a fourth dimension - time."   

 "We all know about time, " another member of the group said. "Time passed."

 "I do not agree,"  the time traveler said, "Length, breadth and thickness do not pass. They stay in the same place in space.  We move about them. I can prove that time is the same. It does not pass. We move in time the same way that we move in breadth, length and thickness."

 None of us believed the time traveler, and we argued with him for many hours.

 "If we could travel back in time,"  the scientist said, "We could do things to change the future." 

 "If we could travel forward in time," the doctor(博士) said, "we could do things that change our present." 

 The time traveler smiled, "It is clear," he said, "that there is only one way I can show you that I am right. We must do an experiment. Please wait here." 

 He left the room and soon returned, carrying what looked like a clock.

 "This is a model of a time machine. It took me two years to make it," the time traveler said. "I want all of you to understand that when I start the machine, it will immediately travel in time and disappear from the present." 

 He turned to the youngest of all. "Give me your hand," he said.

 The young man put out his hand. The time traveler took it and placed it on the machine. Immediately, there was a sudden wind, and the little machine disappeared.

 I was certain this was not a trick, but the doctor was not so sure.

 "Are you asking us to believe," he said, "that the machine is now in a different time?" 

 "Certainly! In my laboratory, a full-size machine is almost complete. As soon as it is complete, I shall send myself on a journey through time. Would you like to see my machine?"

 "Are you serious about this?" the doctor asked.

 "I have never been more serious about anything," the time traveler said, "Come." 

We followed him to his laboratory. There, we saw the actual machine, not quite complete, but large enough for a man to sit in.

    Mr and Mrs Brown are from America. They are now teaching English in Beijing .Their son Jack is with them. Jack speaks English. They want him to learn some Chinese. Jack is in Grade Three in a Chinese school .He likes to play with(玩耍) Chinese children every day. He listens to Chinese, speaks Chinese, reads books in Chinese and writes in Chinese. He is good at his Chinese.

    Homeless people face a lot of challenges, - such as not having enough to eat and no job opportunities. Some of the most basic challenges, - however, -are not having clean water and toiletries (卫生用品)-a big problem for homeless teens. That encouraged a young researcher to invent a multi-purpose product to help these teens.

    "I was born into a life of volunteering," said 13-year-old Leia Gluckman. And that's true. Her mom is a president of an organization providing help for homeless teens. Leia and her brother have volunteered there for years. When she was a young girl, Leia helped serve food where teens were eating. Now she's a teenager herself, and she's managing the toiletry and clothing work there.

    From her work at the center, Leia noticed that teens asked for some toiletries more than others. What they needed most often were toothpaste, body powder (粉)and shampoo(洗发水).Leia wondered whether she could create a product to serve all three purposes.

    It would need to take away dirt and oil from skin and hair. It would need to clean teeth. Also, it would need to kill bacteria (病菌)without being harmful to people. She wanted her ingredients (产品成分)to be natural, to be able to break down easily and to taste and smell pleasant. Moreover, this product had to be low﹣cost and have a long shelf life.

    Leia started by going to stores and looking at the ingredient lists for toiletries. Then she tried eight different ways. She tested each way to see how well it worked.

    Not all of them worked well. But she finally decided on three. Each includes salt and baking powder. Salt helps clean teeth and skin; baking powder helps take in bad smells. She also has some other recipes which include some special materials that give her products different tastes and smells, which would let teens choose a product based on personal preferences.

    It wasn't easy, but Leia came up with some model products. She presented them at the finals of Broadcom MASTERS science competition.

    Leia wants to develop her products further. "Could it possibly be used to drive away mosquitoes (蚊子)?" she wonders.

    "Science offers a way to go about solving problems and helping people," says Leia. And she thinks her products could benefit a great number of people, not just the homeless. Anyone in an area with little or no chance to get clean water could find her products useful, maybe refugees (难民) and soldiers who are sent to places without running water.

    Jim goes to Tokyo. He wants to see his aunt. But when he walks out of the station, he can't find his way. The city is now quite different. He sees a man outside a police station, so he goes up to ask him for help. The man looks at him for a long time, then says, “I'm sorry, sir. I'm from another city. I'm standing here and want to find a policeman. He may tell you the way.”