Which of the following organs is most affected by a deficiency of $O_2$ in humans?

What is the cause of lung cancer in coal miners?

The state during which the respiratory centre is inhibited is termed as:

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 $R$?

What are the symptoms of $Altitude$ $Sickness$?

In this disease,the respiratory surface area decreases.