What is the signet ring-shaped cartilage?

Which is a common passage for swallowing food and breathing?

Analogy type questions:
$(1)$ Sponges,Coelenterates : Respiration through entire body surface :: Insects : ....
$(2)$ Larynx : Cartilaginous box :: Epiglottis : .......

Identify the odd one out from the following structures.

Diaphragm is found in

The roof of the nasal cavity is formed by which bone?