Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions.The increase in urbanization causes different problems. Air and water pollution are amongst the major issue we have to tackle.In the first place, cars, factories and burning waste emit dangerous gases that change the air quality in our cities and pose threats to our health. Dangerous gases such as carbon dioxide and nitrogen oxides cause respiratory diseases, for instant, ...

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

The increase in urbanization causes different problems. Air and water pollution are amongst the major issue we have to tackle.

In the first place, cars, factories and burning waste emit dangerous gases that change the air quality in our cities and pose threats to our health. Dangerous gases such as carbon dioxide and nitrogen oxides cause respiratory diseases, for instant, bronchitis and asthma. Those are also proved to have long-term effects on the environment.

Furthermore, with the increased population, it becomes difficult to manage the waste generated in cities. Most of the waste is discharged or dumped into rivers or onto streets. The waste pollutes water and makes it unfit for human consumption. Subsequently, it becomes more and more difficult for city dwellers to get clean water. Some cities in Africa are unable to provide adequate water supply because most of the water is lost in pipe leakages. In fact, most city dwellers in developing countries are forced to boil their water or to buy bottled water, which is very expensive.

There are several actions that could be taken to eradicate the problems described above. Firstly, a simple solution would be joining community efforts to address problems affecting your city. Ask your parents, friends and relatives to join in as well. These efforts might include clean-up campaigns, recycling projects and a signature campaign to ask the government to do something about the situation. A second measure would be encouraging your teacher to talk about these problems and to discuss how young people can help to solve them. Finally, writing to local organizations working on these issues for ideas on how you can contribute to solve them.

The word those in paragraph 2 refers to ____.