What will happen if:
$(a)$ Peristaltic movements do not occur all along the oesophagus?
$(b)$ There are no platelets in the blood?
$(c)$ Rings of cartilage are not present in the trachea?

(N/A) If peristaltic movements do not occur,the food will not be pushed forward into the stomach,leading to an inability to swallow or digest food properly.
$(b)$ If there are no platelets in the blood,the blood will not clot in the event of an injury,which could lead to excessive and potentially fatal blood loss.
$(c)$ In the absence of rings of cartilage,the trachea (windpipe) would collapse during inhalation because the air pressure inside the tube decreases,potentially obstructing the airway.