When we think of bicycles, we think of fun and the outdoors. Bicycles give riders the freedom to explore and enjoy the environment and its surroundings. 【小题1】

Most people know that riding bicycles is environmentally friendly. 【小题2】 If you are riding a bike, you are helping to reduce air and noise pollution.

Bikes are becoming more and more popular across the world. In fact, they are becoming more than just a fun pastime (娱乐). 【小题3】 For many people around the world, access to markets and schools would not be accessible without a bike.

【小题4】 Some cities, such as Paris and Barcelona, have not only built bicycle lanes but also have introduced a system of renting bikes. You can rent, or use a bicycle in one area of the city and drop it off in another area of the city. Paris now has thousands of bikes for public use, with bicycle stations located throughout the city.

Some South American cities, such as Bogota in Colombia, have a weekly car-free day. 【小题5】 On these days, the traffic-related air pollution from old buses and trucks is greatly reduced.

It seems that the bike is a force for good, providing solutions for cleaner cities without leaving a serious environmental footprint.

The world is a greener place than it was 20 years ago. Recent NASA satellites data(2000—2017) have shown that human activities in China and India dominate this greening of the planet, thanks to ambitious tree-planting programmes in China and intensive agriculture(集约农业) in both countries.

The researchers from Boston University found that global green leaf area has increased by 5 percent in the new century, an area equal to all of the Amazon rainforest. China alone accounts for 25% of the global net increase in leaf area with only 6.6% of global vegetated area. China's contribution comes in large part from its programmes to conserve and expand forests, taking up about 42 percent of the greening. The greening from farmlands in China is about 32%, but that in India is about 82%.

Rama Nemani, a research scientist at NASA's Ames Research Centre and a co-author of the study said, ''When the greening of the Earth was first observed, we thought it was due to a warmer, wetter climate and fertilisation from the added carbon dioxide in the atmosphere. But with data from NASA satellites, scientists realised that humans are also contributing, which was all against our expectations. ''

Nemani sees a positive message in the new findings. ''Once people realise there is a problem, they tend to fix it, '' he said. ''In the 1970s and 1980s in India and China, the situation around vegetation loss was not good. In the 1990s, people realised it, and today things have improved. Humans are incredibly resilient. That is what we see in the satellite data. ''

However, the researchers rang bells as well. They said that the gain in global greenness did not necessarily make up for the loss of natural vegetation in regions like Brazil and Indonesia.