Read the following passage and mark the letter A, B, C or D on your answer sheet toindicate the correct answer to each of the following questions.

When people hear the word "city", they usually imagine concrete, neon signs, and lots of air pollution. Thanks to some clever and concerned architects, this image is starting to change. The concept of green cities aims to bring some beauty from rural environments into urban areas. It is not only about looking better though. Green cities are also trying to improve the efficiency of cities and raise the standard of living for people who stay in them.

The term "green cities" refers to cities where builders take into account several environmental factors before those cities are constructed or redesigned. For starters, green cities are designed to be more physically appealing than traditional cities from the past. In addition, the mobility of citizens should be considered, so public transportation can be more convenient and travel time to work can be reduced. Energy sources should also be evaluated with the goal of minimizing air pollution.

When it comes to going green, the city of Barcelona is far ahead of its time. Since 1859, its designers have consciously tried to create sustainable urban designs. Then in 1992, the city received a welldeserved makeover before hosting the Olympic Games. In recent years, Barcelona has upgraded its transportation system. This has reduced air pollution and more workers are using public transportation instead of their own vehicles. Barcelona also boasts one of the best recycling programs in the world. Visitors will find clear color coded trash bins throughout the city where they can put all of their materials.

What does the term "mobility" in paragraph 2 mean?