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 Single plane skywriting has largely been replaced by multi-plane "skytyping" , a computer-controlled method involving puffs of smoke from a row of aircraft.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.

Exposure to sunlight produces vitamin D in our skin. This is 【小题1】 we call vitamin D the “ sunshine vitamin”. Vitamin D is good 【小题2】 everybody. In fact, research shows this “sunshine vitamin” could help women with breast cancer live longer.

Breast cancer 【小题3】 (patient) who have high blood levels of vitamin D have a 【小题4】 (good) prognosis (预后) than women who don’t. Researchers found that these women had less aggressive cancers. They were also 30 percent less likely 【小题5】 (die) from the cancer or to get it again.

Besides fighting breast cancer, vitamin D helps the body in other ways. It controls how the body absorbs calcium. It also makes sure the body’s immune system works 【小题6】 (normal) .

Getting enough vitamin D 【小题7】 (be) important for the normal growth of bones. If you don’t get enough, you are at risk of developing osteoporosis, a disease 【小题8】 makes your bones fragile, brittle, or easy to break.

Vitamin D may help reduce your risk of developing heart disease, according to a 2008 study 【小题9】 (publish) in the journal Circulation. And, it may also help protect you against getting the flu.

Other studies have shown that vitamin D might help people 【小题10】 (suffer) from depression.

   According to a recent report, about 15% of the people in the UK are members of gyms. But are they more likely to be fit?

A study found that gym members were 14 times more active than people who didn’t belong to any health club. Gym members did six hours more exercise a week, and this activity did make them fitter than non-gym members. They also spent less time sitting down every day than non-gym members. The results were the same for men and women.

The study included 405 people between the ages of 30 and 64, and the main characteristics of those who were gym members were the same as those who were not. ''But gym members did more training than non-gym members, '' said the lead author, Elizabeth Schroeder of the University of Illinois.

While it might seem clear that gym members exercising more are healthier than non-members, Schroeder says this has not been directly shown before. However, the study is only designed to show a tie between gym membership and more exercise. It may be that active people like to join gyms. In the study, people who exercised as much as gym members were also in good health.

You can get the same benefits wherever you exercise. This study shows a gym membership can make you do more exercise, but other research shows that exercising outside has other help. Outdoor activities can make you feel happy about life—especially if you run through a forest.

Outdoor exercise is also more enjoyable than going to the gym. The first five minutes of outdoor exercise is especially helpful in making people feel good. But Schroeder says that a gym may also encourage greater exercise because it can be social and fun.