An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure,which forces the air from outside to move into the lungs. This process is known as:

Pick the correct statement.

Expiration occurs due to

Which muscles help us to increase the strength of inspiration and expiration?

An $A$ in the pulmonary volume $B$ the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from $C$ to move into the lungs,i.e.,$D$. Choose the correct options for the blanks $A, B, C$ and $D$ to complete the above statement with reference to $NCERT$ textbook.

Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because