Just like humans, birds rely on sound to communicate, too. Often, birds recognize their mates or young by sound rather than sight. Hungry young birds use begging calls to let their mothers know it is feeding time, and warning calls are other sounds given out frequently by the adults. In addition to all these regular calls, some male birds develop beautiful songs intended（打算）to attract the females.

A new study carried out by an American university shows that songbirds practice their songs even in their sleep. The research team discovered that the electrical brain activity of the birds that were asleep was similar to the brain activity produced when the birds were awake and singing. Clearly the bird stores a song after hearing it, then practices it later in its sleep. Scientists now believe the birds dream of songs to help them master the fine art of singing and that sleep plays a key role in the learning process！

It is commonly known that many songbirds learn to sing by listening to adult birds of the same species. If taught the song of an adult of another bird species, the chick grows up singing the new song and passes on the foreign song to its chicks. For instance, researchers carried out an experiment in which a male bullfinch（红腹灰雀）was raised by a female canary（金丝雀）. The bullfinch soon learned the canary's songs and when it was later mated to a female bullfinch, Mr. Bullfinch taught his children the canary's songs.

Early last year, a British survey of London's songbirds showed that the city's birds are losing their melodies. Birds could hardly hear one another over the traffic noise；as a result they had difficulty in learning songs and communicating with potential mates. And instead of copying the sweet notes of the adults, chicks were copying sounds, which they heard most often—namely car horns（喇叭）and mobile phones！

   Skywriting is a form of advertising in which a pilot is bound to spell out a brief slogan or catchphrase in letters formed by smoke. In general, a customer would choose a specific place and time for the skywriting to appear. The message would only last as long as winds are relatively calm and the sky is clear. Single plane skywriting has largely been replaced by multi-plane "skytyping" , a computer-controlled method involving puffs of smoke from a row of aircraft.

The first official skywriting show took place over New York City in November of 1922. A skywriting pioneer and Royal Air Force（RAF）pilot named John Savage sat with the president of the American Tobacco Company, George Hill, as a fellow RAF ace pilot named Captain Cyril Turner flew into position over New York City. Captain Turner spelled out "HELLO USA CALL VANDERBILT 7200" in white smoke. Over47,000 people called the number, which happened to be the Vanderbilt Hotel where George Hill was staying. Hill became convinced that the skywriting advertisements would work well to promote his Lucky Strike cigarettes.

Skywriting continued to grow in popularity as both an advertising medium and a personal message service. Customers could request anything from "Eat at Joe's" to "Will You Marry Me？"Messages and slogans would naturally have to remain short, but even a simple phone number could produce a lot of curious potential（潜在的）customers for a small investment.

The development of the national highway system after WW Ⅱ spelled the beginning of the end for the skywriting industry. Instead of posting a few words in the sky, advertisers could now fill entire billboards with all sorts of pictures. Thousands of captive audience would pass by these new advertising signs every day, unlike the precious few who would come across a typical skywriting message. Many aerial（空中的）advertising companies turned to permanent banners（横幅）pulled behind low-flying aircraft instead.

Some skywriting is still performed today, although only a select number of pilots have the skills necessary for the job.

   In the United States alone,over 100 million cell-phones are thrown away each year.Cell-phones are part of a growing mountain of electronic waste like computers and personal digital assistants.The electronic waste stream is increasing three times taster than traditional garbage as a whole.

Electronic devices contain valuable metals such as gold and silver.A Swiss study reported that while the weight of electronic goods represented by precious metals was relatively small in comparison to total waste,the concentration（含量）of gold and other precious metals was higher in So-called e-waste than in naturally occurring minerals.

Electronic wastes also contain many poisonous metals.Even when the machines are recycled and the harmful metals removed,the recycling process often is carried out in poor countries,in practically uncontrolled ways which allow many poisonous substances to escape into the environment.

Creating products out of raw materials creates much more waste material,up to 100 times more,than the material contained in the finished products.Consider again the cell-phone,and imagine the mines that produced those metals,the factories needed to make the box and packaging（包装）it came in.Many wastes produced in the producing process are harmful as well.

The U.S Environmental Protection Agency notes that most waste is dangerous in that"the production, distribution,and use of products-as well as management of the resulting waste-all result in greenhouse gas release." Individuals can reduce their contribution by creating less waste at the start-for instance,buying reusable products and recycling.

In many countries the concept of extended producer responsibility is being considered or has been put in place as an incentive（动机）for reducing waste.If producers are required to take back packaging they use to sell their products,would they reduce the packaging in the first place?

Governments' incentive to require producers to take responsibility for the packaging they produce is usually based on money.Why,they ask,should cities or towns be responsible for paying to deal with the bubble wrap（气泡垫）that encased your television?

From the governments' point of view,a primary goal of laws requiring extended producer responsibility is to transfer both the costs and the physical responsibility of waste management from the government and tax-payers back to the producers.

   The idea of being able to walk on water has long interested humans greatly. Sadly, biological facts prevent us ever accomplishing such a thing without artificial aid---we simply weigh too much, and all our mass pushes down through our relatively small feet, resulting in a lot of pressure that makes us sink.

But fortunately there is an alternative : cornflour. By adding enough of this common thickening agent to water (and it does take a lot), you can create a “non-Newtonian” liquid that doesn’t behave like normal water. Now, if the surface of the water is hit hard enough, particles(粒子）in the water group together for a moment to make the surface hard. Move quickly enough and put enough force into each step, and you really can walk across the surface of an adequately thick Liquid of cornflour.

Fun though all this may sound, it’s still rather messy and better read about in theory than carried out in practice. If you must do it, then keep the water wings handy in case you start to sink--and take a shower afterward!