Which is the most important muscular structure in the respiratory system of a rabbit?

Pick the correct statement.

Define the following terms:
$(1)$ Inspiration
$(2)$ Expiration

When do the expiratory muscles contract?

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.

The normal shape of the diaphragm is