【推荐1】The fireworks that you see are most likely made in China. The country that makes90% of the world’s fireworks is also where they were invented. Most historians believe that the Chinese used firecrackers as early as the second century B. C.

Many countries hold grand fireworks show at their important celebrations. Canadians, for example, put on fireworks show every July 1 to celebrate their own national birthday, as the French do on July 14 to mark the anniversary of their revolution. But the United States of America imports most of the world’s fireworks, spending more than $650 million on them per year. The Walt Disney Co. alone buys about $50 million worth.

A mixture of gunpowder and other flammable compounds(混合物) causes fireworks to explode across the sky in all those pretty colors and fun shapes. Copper, for instance, burns bright blue while strontium(锶) creates deep red. Together, they produce purple. But the outlines fireworks form depend on the placement of these compounds inside their casing (known as the shell), as well as the shape of the shell itself.

For centuries the only way to set off fireworks was by hand, but computer controlled equipment came out in the 1980s. Automation means more precisely timed explosions, making the displays more satisfying, not to mention safer.

As you might imagine, setting off fireworks can release harmful substances into the air. For example, a chemical that has been linked to thyroid(甲状腺) problems. “Environmentally friendly”   fireworks were developed at the request of the Walt Disney Co. after it received smoke complaints from neighbors of Disneyland. Nowadays, an even more eco-friendly alternative to traditional fireworks is being increasingly adopted: using small aircrafts without pilots to trace flashy patterns in the sky. With them, there’s also a much smaller risk of causing wildfires. The eco-friendly fireworks industry is expected to grow almost 20% between now and 2027.

【推荐2】Designing playgrounds is a tough job. First, they have to be fun. But they also have to be safe, affordable, and accessible. Kids with disabilities can use and enjoy accessible playgrounds. Some people can’t get around without the help of a wheelchair or walker. Others have trouble climbing, jumping, or balancing. How do you design a playground for people with such different disabilities?

One way is to provide accessible equipment. Think about swings. They’re a popular piece of playground equipment. But most swings are just a thick flat piece of rubber to sit on and two chains to hang onto. Kids who have trouble controlling their muscles may fall off and get hurt. How would you solve this problem?

It’s not just equipment that can cause problems for kids with disabilities. Even the surface of a playground is important. The ground under many playgrounds isn’t smooth. It’s covered with loose wood or rubber chips. This makes the ground softer in case someone falls, but the loose material is hard for some people to cross — especially people in wheelchairs. Some playgrounds solve this problem with smooth, rubber surfaces. These are great for everyone.

It takes creative thinking to come up with designs that work for everyone. Take a sandbox for example, is it low to the ground? Most sandboxes are. These are fun for kids who can easily sit or kneel on the ground. But what about kids who can’t?

Now design three sandboxes. One is on the ground, and two others are on raised platforms. One is at knee level, and the other is at waist level. Kids who can sit, stand, and kneel can play at any of them. Kids in wheelchairs, or others who can’t easily play on the ground, can use the raised ones. If all three sandboxes are right next to each other, all sorts of kids can play together.

While you’re looking at playgrounds with a designer’s eye, you’ll probably notice that some aren’t very accessible. Many old playgrounds weren’t designed with a range of abilities in mind. It can be expensive to change that. Still, accessible playgrounds are becoming more common. Doesn’t every kid deserve to have fun?

【推荐3】Arouca Geopark in Portugal has announced that visitors are free to visit its record-setting bridge, the 516 Arouca Bridge. Though it’s quite high, it’s the length of the bridge that has set a record. It’s the world’s longest hanging bridge for walkers.

The bridge runs between two mountains in Arouca Geopark. The “516” in its name comes from the fact that it’s 516 meters. Until the 516 Arouca Bridge was completed, the longest hanging bridge for walkers was the 494-meter-long Charles Kuonen Bridge in Randa, Switzerland. To replace an older crossing that was damaged by falling rocks, it was opened to the public five years ago, as the website for what is now the world’s second longest hanging bridge says.

The 516 Arouca Bridge, started in May, 2018, is made mainly of metal. It cost $2.8 million and took two years to complete. However, it was not until one year later that the bridge was officially opened. It is a little scary to walk on. The sides and bottom of the bridge are built with a metal grid (网格) and it’s easy to see through it. At its highest point, the bridge is 175 meters off the ground. Far, far below is the rushing Paiva River.

Arouca Geopark is famous for its beautiful natural scenery and the many outdoor activities. Arouca’s leader, Margarida Belém, says proudly, “There’s no other bridge like this one in the world.” All of the city leaders think the bridge can attract people from all over the world for a lot of different reasons. Some might come for the scenery. Others might come to see how the bridge was built. But perhaps most will come to enjoy the safe, but scary experience of walking across. Its website describes the walk as “the most exciting 516 meters of your life”.