Each one of us shares this planet with more than seven billion others, and we all need ______. People and products need to move from city to city and from country to country. However, we all know ______ most cars, motorcycles, boats and planes cause air pollution. They are also ______. This is a serious problem in many cities. ______ inventors are coming up with creative ideas to try to reduce the pollution and noise.

In many cities around the world, motorcycles are very ______. Now Vietnam has around 33 million motorcycles and China has almost 100 million. Motorcycles are a cheaper way to get around a city than ______. Yet air pollution is a growing problem. In large cities, people ______ it is difficult to breathe. To solve these problems, a US company designed an environmentally friendly motorcycle. It uses electricity as fuel (燃料). As a result, there is ______ pollution. It’s also quiet and fast. This makes ______ a good choice for getting around a city.

The Italian city of Venice is a city with only a few ______. There are no cars in the city centre. ______ cars, water taxis and buses carry people along the city’s canals (运河). However, they cause pollution, ______ to the water. British engineers Dick and Jem designed a solar-powered (太阳能的) water taxi. The water taxi ______ run for a day after being recharged (充电).

Planes also cause air and noise pollution. Designing an environmentally friendly airplane is a real ______. Some airplane companies have ______ to solve the problems. Swiss engineers have gone one step further. They developed a solar airplane. This plane holds the world record for the longest solar-powered flight-1, 541 kilometres from Arizona to Texas in America.