Carbon monoxide $(CO)$ is harmful to humans because:

Asthma is a respiratory disease caused by which of the following?

$A$ - Smoking is associated with increased incidence of cancer of lung.
$R$ - It increases $CO$ content in blood and reduces the concentration of haem-bound oxygen.

Chronic respiratory disorders like $.......$ are caused by pollen grains.

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

Assertion $A$: Pneumonia is a serious respiratory disease.
Reason $R$: The accumulation of fluid in the alveoli and bronchioles prevents sufficient oxygen from reaching the lungs.
Which option is correct for Assertion $A$ and Reason $R$?