Partial pressure for oxygen and $CO_2$ is represented as

Which of the following is correct regarding the partial pressures of gases ($PO_2$ and $PCO_2$) in different parts of the human respiratory system?

The partial pressure of oxygen in the alveolar air is

What is the value of $pCO_2$ in atmospheric air,alveoli,and tissues respectively?

The low partial pressure of oxygen $(PO_2)$ in the body cells results in:

Identify $A, B$ and $C$ in the given diagram and choose the correct option accordingly.