Question

asthma
asthma is a common disease of the lungs. when people have asthma, their airways, or breathing tubes, swell up and get sore. when the airways swell, smoke and dust can easily bother them. as a result, the muscles of the airways get tighter. the tight muscles cause the breathing passages to become narrower, so air cant get through. thus, it can sometimes be difficult for people with asthma to breathe. luckily, there are medicines that open the airways and help people feel better.
what is the main, or central, idea of the passage?
in asthma, problems with peoples airways lead to difficulty with breathing.
medicines help people with asthma by opening airways that have swelled up.
smoke and dust can be a problem for people with swollen airways.

Explanation:

The passage first introduces asthma as a lung disease. It then details how airway swelling (a key problem in asthma) leads to muscle tightening, narrower breathing passages, and thus breathing difficulty. The other options (about medicines and smoke/dust) are details supporting the main idea.

Answer:

In asthma, problems with people's airways lead to difficulty with breathing.