Personal planes which can take off noiselessly from the back garden will be possible within two years.

    Lilium Aviation is inventing an electric two-seater airplane which  takes just 20 hours to learn to fly and can travel at speeds of  250mph.More importantly, the small plane, which weighs just 25kg, can take off vertically which means it does not need to fly from an airport, but could be parked outside a house or in a garden. The company says the design will “open the door to a new class of simpler, quieter and environmentally friendly planes” and will be possible from 2018.

    “Our goal is to develop an airplane for use in everyday life,” said Daniel, CEO and one of the company's four founders. "We are going for a plane that can take off and land vertically and does not need the difficult and expensive infrastructure of an airport.

    Although helicopters offer a choice, they are very noisy and difficult to fly and require expensive licenses. They also have no backup if the rotor fails, making them costly to build and keep. While firstly limited to airfields, the Lilium airplane will eventually take off vertically from almost anywhere – even from back gardens – it needs only an open flat area of 50 ft. by 50ft (15 m x 15m).

    The plane is classed as a Light Sport Aircraft for two users, with the pilot's license requiring 20 hours' minimum training – almost like taking a driving license. It is intended for fun flying during daylight, in good weather conditions and in least crowded airspace up to 3 km altitude. The airplane would have to follow the same flight laws as helicopters.

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    When a computer works on a group of programs, it can get very hot. Cooling the computer can cost a lot. So some scientists wonder what would happen if the heat from the computer could be used.

    Large Internet companies (公司）such as Google and Microsoft have thousands of computers. As these computers deal with information, they produce lots of heat, so they need huge cooling systems(系统）. These systems send the heat into the air.

    A company in Holland(荷兰） thinks paying to make the computers work and then paying again to cool them are a waste of energy. So the company developed a special device—the e-Radiator.

    Boaz Leupe, head of the company, says the e-Radiator works as a heating system and saves money. He explains that the energy is used twice—once to heat the home and once to cool the computer and that the users don't have to pay to cool their computers.

    Five homeowners in Holland are testing the heating system in their homes.

    "We pay for the computer using, so, in that way, homeowners get heating for free," Boaz says.

    Jan Visser is one of the homeowners. "If you use the computer more, the e-Radiator produces more heat," he says. "It can't provide enough heat if you don't use your computer often." But he is ready to try it. It's a great help for his family.

    The company says e-Radiators produce heat temperatures of up to 55℃. It says the system could save its users about $440 a year.

    Bruce collected the papers Clive collected the cans

    And Mort tied them with string And Dean washed them all clean

    Jason helped Bruce carry the papers Ruby helped Clive carry the cans

    All the way to the recycling(回收) bins All the way to the recycling bins

    When we recycle, we help the plants

    We help the creatures, from eagles to ants

    We help make the world a healthier place

    For one and for all in the human(人类) race

    Height is just one of the thousands of features your genes (基因) decide. In fact, because you have two parents, your genes provide you a height that usually lands somewhere between the height of each parent. If both your parents are tall, then maybe you will be tall, too, but if you have questions about how tall you're going to be, ask your doctor if he or she can help you find it.

    But genes don't decide everything. For example, eating an unhealthy diet can keep you from growing to your full potential (潜力). Getting enough sleep and enough exercise will help you grow to the right height.

    No doubt (怀疑) you're wondering how fast you should grow .It depends. There's no perfect or right answer. Kids grow about 2 inches (5 centimeters) a year between age 3 and the time when they start puberty (when your body starts changing and becoming more grown up). Your doctor will know how your growth has been going over the years. 2 centimeters here and 2 inches there are not nearly as important as the height you're at now, how you've been growing up to this point, and what other changes your body may be going through.

    Don't be scared if you seem to have grown a lot in a very short time. Everyone has a growth spurt (高峰) during puberty. The age for starting puberty is about 10 for girls and about II for boys. But it can be earlier or later-between 7 and 13 for girls and 9 and 15 for boys.

    You'll usually begin to notice that you're growing faster about a year or so after your body starts to show the first changes of puberty.