Copenhagen, voted as the "Best City for Cyclists" and "World's Most Livable City", has a profound bicycle culture, one that is rooted in almost every Copenhagener's daily life.

For Copenhageners, bicycles are one of the best means of transportation. They are convenient, fast and environmentally friendly. Every morning, when I head to school, I can see a great many cyclists from all age groups riding their well-equipped and beautifully designed bicycles to school or work. What is most unbelievable for me is that even those aged 70 or 80 still prefer biking as their main mode of transportation.

The Danes' passion for bicycles is similar to the Chinese craze for ping-pong or Brazilians' love of football; many great cyclists arise in Denmark who have already achieved great success in the international sporting arena. One example is Larsen Norman Hansen, a Danish professional road and track racing cyclist, who won one gold medal and two silver medals in big events. In addition, bikes are also huge part of the recreational life of many young Danes. One of my Danish friends, Laurits Genz, a 21-year-old Chinese studies student from Copenhagen University, has a hobby of rebuilding old bicycles. He has collected many old bikes from a recycling station near his home and completely restored them, giving them new parts and a fresh coat of paint. He believes that eventually, all of these bikes with that "classic" look are going to be very sought after and valuable.

Some people might wonder why bike-related culture is so universal and popular in Copenhagen, but not as much so in other parts of the world. I would name a couple of reasons: First of all, the infrastructure constructed in Copenhagen is very cyclist friendly. On many roads in Copenhagen, if cyclists can ride their bikes at the speed of 20 kph and remain stable, they can surf through on a wave of green traffic lights through the city without putting a foot down. It's absolutely a great environment. Another factor is the government's friendliness to cyclists. Because of this government policy, bikers enjoy a sort of encouraged state of privilege（特权）, meaning they will stick to this means of transportation even during the coldest winter season. Danes' tendency toward a healthy and environmentally friendly lifestyle also lends itself to choosing cycling.

Petrol and diesel cars may still dominate our roads, but their days are numbered. A recent university study found that current electric cars could be used for 87 per cent of daily car journeys in the US. That figure could rise to 98 per cent by 2020.

One barrier (障碍) to the widespread adoption of electric cars has been ‘range anxiety’ -- drivers’ concerns about using up juice on a journey. While petrol stations are conveniently located across national road systems, the necessary network of electric charging stations is still being developed. Nevertheless, charging points are becoming increasingly common throughout the USA.

Attitudes towards electric vehicles have changed quite considerably over the last few years. Not that long ago, electric cars were met with distrust, and their large price tags drove customers away. Thanks to improvements in battery capacity, recharging times, performance and price, the current generation of electric cars is starting to persuade critics. Plug-in cars   will soon give internal combustion engine models a run for their money.

As well as advancements on the road, electric vehicles are taking to the seas and skies. Electric boats are among the oldest methods of electric travel, having been popular for several decades from the late 19th to the early 20th century before petrol-powered outboard motors took over. Now, the global drive for renewable energy sources is bringing electric boats back. Steps towards electric air travel are also being made, with Airbus and NASA among the organizations developing and testing battery powered planes. The experiments could soon make commercial electric flight a reality.

Electric vehicles do not produce any emissions. Were the US to act on the study’s findings and replace 87 per cent of its cars with electric vehicles, it would reduce the national demand for petrol by 61 percent. However, because of the production processes and the generation of electricity required to charge these vehicles, they cannot claim to be completely emission-free. However, as many countries continue to increase their use of renewable energy sources, electric vehicles will become even cleaner.

Have you ever been on an airplane, minding your own business, and found your eyes filled with tears for no reason? Or perhaps you sat near someone who burst into tears. Is there something happening to your body that triggers (引发) the tears?

There sure is! When you’re inside a flying airplane, you’re miles off the ground. Not exactly a place where humans usually find themselves. The airplane is pressurized (加压) to keep passengers comfortable. But it’s still not the pressure levels that you’ll experience at ground level. It’s a bit like having climbed a pretty high mountain.

The primary tear-trigger is the lower amount of oxygen in your blood. The oxygen levels in the plane are lower than you’ll find on the ground. And it can bring you bad feelings.

Another cause is dehydration (脱水). Because the air in the plane is very dry, we may get dehydrated. And being dehydrated can have all kinds of harmful effects on your 30,000-foot-high body, which is making you have bad feelings like sadness and worry. In fact, there is a spiritual reason, too! Even if you’re not afraid of planes, it’s a high-stress situation. Taking a flight often involves saying goodbye to someone in the place you’re leaving. You can also be worried about plane crash or losing your baggage.

You can drink plenty of water before your flight to fight back your tears. You can also keep your mind busy with a puzzle or brain game. And if you’re going to watch a movie, maybe choose one that’s a bit more relaxing. In short, make flying a more pleasant and less stressful experience.