Read the passage and choose the correct answer A, B, C, or D.

Twenty years ago, people tried to leave the suburbs for cities but nowadays many people are reluctant to make such a move. They say that compared to suburban areas, city life has many drawbacks.

The high cost of living is the first disadvantage. The bigger the city is, the higher the living cost is. Accommodation and petrol are expensive. Food and drinks are also pricey. Apart from that, city people seem to suffer from more noise and air pollution. The densely populated neighbourhoods, busy traffic, and big construction sites make cities noisy and dusty. These are harmful to people's health, such as increasing their stress levels, disturbing their sleep and making them suffer from breathing problems.

Lack of space is another drawback of city life. House prices are high in the city, so people tend to live in smaller houses or in apartment blocks. Many cities lack spaces for outdoor activities; therefore, teenagers often hang out at shopping malls or in entertainment complexes instead of doing sports outdoors.

The cities' authorities are trying to overcome these problems. However, they still have a long way to go before they can reduce living costs and pollution, and increase green space to make all cities in the world more liveable places.

What is the passage mainly about?