Read the following passage and answer Questions.

An environmental issue that concerns us all is the problem of air pollution. We, the humans, have the choice of what we want to eat, drink, choices for lifestyle but unfortunately, we don't have the alternative for what we want to inhale- clean air or polluted one. Everything in the air is inhaled by all living beings in those surroundings.

Air pollutant refers to substances which are not a part of air composition and are present in an amount exceeding the normal concentrations. These pollutants can be either in the form of gas or a particulate matter. These harmful gases are carbon monoxide, carbon dioxide, ozone and oxides of sulphur and nitrogen. The common particulate pollutants are the dusts of various inorganic or organic origins. Although we often talk of the outdoor air pollution caused by industrial and vehicular exhausts, the indoor pollution may prove to be just as or even more important cause of health problems.

The composition of air is about 79 percent nitrogen and 21 per cent oxygen and the other gases forming a very small fraction. One feels suffocated in a closed environment due to lack of oxygen. Carbon dioxide exhaled out of lungs may accumulate in a closed and overcrowded place and contribute to feeling claustrophobic. The conventional way of burning fuel or coal to heat up a room may also lead to exposure to poisonous gases such as carbon monoxide.

A poorly ventilated house has a vague constellation of symptoms described as the sick building syndrome. This syndrome is common in big cities with the small houses, which are generally over furnished. It is characterised by a general feeling of malaise, headache, dizziness and irritation of mucous membranes. It may also be accompanied by nausea, itching, aches, pains and depression. Some of the indoor pollutants concentrations that exceed those of the outdoors, include gases such as carbon monoxide, carbon dioxide, oxides of nitrogen and organic substances like spores, formaldehydes, hydrocarbon aerosols and allergens. The sources are attributed to a variety of construction materials, insulations, furnishing, adhesives, cosmetics, house dusts, fungi and other indoor products.

Choose the correct answer from options given below to complete the following sentence.

From the passage it may be concluded that air pollution is _________ .

a combination of unwanted particulate and gaseous matter