1. fossil fuels, cause damage to

e.g.  The use of fossil fuels can cause damage to the environment, possibly because it creates air pollution.

2. apartment blocks, overcrowding

e.g. Apartment blocks, which make the most of the land and space, help solve overcrowding in cities.

3. disadvantaged background, social status, arduous, rewarding

e.g. People from disadvantaged backgrounds can improve their social status by working hard and it seems an arduous but rewarding process.