What is the cause of asthma?

In heavy smokers,the alveoli of the lungs are enlarged and damaged,which reduces the surface area for the exchange of respiratory gases. This condition is called:

Ravi,who lived at sea level,had around $5$ million $RBC$ per cubic millimeter of his blood. Later when he lived at an altitude of $18,000 \ ft$,he showed around $8$ million $RBC$ per cubic millimeter of blood. This is an adaptation because

$A$ person involved in stone masonry work is likely to suffer from . . . . . . .

Accumulation of fluoride in plant leaves causes

What is correct for emphysema?