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

During respiration,if the volume of the thoracic cavity of a rabbit is maximum,then:

Given below are events occurring during inspiration. Select the correct order of sequence from the options given below.
$(I)$ Air from atmosphere rushes into lungs.
$(II)$ Thoracic volume increases.
$(III)$ Intercostal muscles contract and ribs along with sternum move upward and outward.
$(IV)$ Diaphragm becomes flat and goes downwards.

In a minute, a normal healthy human adult respires: (in $\times$)

Explain the process of inspiration under normal conditions.

Lung ventilation movements are due to