Answer:
It is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily. Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs.
Air pollution is the answer. The substances in the air could be pollutants which can harm your airways which can be really harmful to an asthmatic. I personally know because i have asthma myself.
Hope I hepled :)
The greenhouse effect is related to the increase in the average surface temperature which is considered "global warming". Global warming is the result of an increase in gases like methane, carbon dioxide, and other factors that lead to a rise in the planet's temperature.