Intercostal muscles are found in ...........

During swallowing,the glottis can be covered by a thin elastic cartilaginous flap called $A$ to prevent the entry of food into the larynx. The trachea is a straight tube extending up to the $B$ cavity,which divides at the level of the $5^{th}$ thoracic vertebra into right and left primary $C$. Choose the correct option for $A, B$,and $C$ from the given four options to complete the above statement with reference to the $NCERT$ textbook.

Select the $INCORRECT$ statement.

What is the number of tracheal cartilaginous rings in humans?

What is the function of the liquid present between the pleural membranes?

The lungs are covered by which of the following?