Read the following passage and answer the five questions that follow.

According to the World Health Organisation (WHO), air pollution is now comparable to other global health risks like unhealthy diets and smoking tobacco. It is recognised "as the single biggest environmental threat to human health". WHO guidelines, which are not legally binding and intended as a reference for policymakers, advocacy groups and academics, stipulate permissible concentrations of six pollutants known to have impacts on health: two types of particulate matter known as PM_2.5 and PM₁₀, as well as Ozone, Nitrogen dioxide, Sulphur dioxide and Carbon monoxide. The guidelines could also send a message to the wider public about lifestyle and business choices - whether it is driving cars and trucks, disposing of garbage, working in industrial jobs or farming. WHO says the main human-generated sources of air pollution can vary geographically but include the energy and transportation sectors, as well as waste dumpsites and home cooking and heating. It advised people to do their part by changing their lifestyles - not running car engines uselessly; avoiding use of plastics that could end up being incinerated; and walking, riding bikes or using public transportation to get to work.

It should be noted that "because of air pollution, the simple act of breathing contributes to 7 million deaths a year. Almost everyone around the world is exposed to unhealthy levels of air pollution". The harmful health effects of air pollution kick in at lower levels than previously thought, the World Health Organisation has said as it has set a new standard for policymakers and the public in the first update of its air quality guidelines in 15 years. Since the last update of the WHO recommendations, better monitoring and science have cleared up the global picture about the effects of six major air pollutants on human health. According to the agency, 90% of the world's people already live in areas with at least one particularly harmful type of pollutant.