The key answer of exercise 3

a)

• Para 2 → One effective solution is for people to leave their cars at home and use public transport instead.
• Para 3 → Another solution is to plant more trees in urban areas.
• Para 4 → Thirdly, it is important to save energy.
• Yes, each topic sentence introduces a new topic.
• Yes, the supporting sentences in each paragraph further explain the topic sentence.

b)

• Para 2 → One useful solution could be to encourage people to use public transport rather than their cars.
• Para 3 → A second effective solution would be to plant more trees in out towns and cities.
• Para 4 → Another way to solve the problem of air pollution would be to cut down on the amount of energy we waste.