b. dust or pollen
Dust and pollen are common triggers for asthma attacks. Allergens like these can cause inflammation and irritation in the airways, leading to asthma symptoms. While antigens can also trigger allergic responses, dust and pollen are more directly associated with asthma. Blood cells are not triggers, and SARS is a viral infection that can worsen asthma symptoms but is not a direct trigger like allergens are.