Human lungs are negative pressure lungs. This means that:
The lungs are always at a lower pressure than the atmosphere
The lungs are always at a higher pressure than the atmosphere
The pressure in the lungs is always equal to the pressure in the atmosphere
None of the above
In negative pressure breathing, the pressure inside the lungs is lower than the atmospheric pressure, which allows air to flow into the lungs.
Option 1 is the correct answer.