Number of alveoli in the human lungs has been estimated to be approximately

Which one of the following has the smallest diameter?

During the act of swallowing,which of the following structures prevents the food bolus from entering the glottis?

The nasal cavity and the oral cavity are separated from each other by the:

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.

Diaphragm is a dome-shaped muscular structure which separates