Q) After a forcible expiration, your lungs won't collapse. explain?

Dear Student

The lungs do not collapse even after forceful expiration as the lungs never become empty.There is always some amount of air left in the lungs which is known as residual volume. 
Also, the presence of C-shaped cartilaginous rings in the tracheae prevents the lungs from collapsing even after a forceful expiration.

Regards