Why is it important that the trachea is reinforced with cartilage rings?

The Trachea is reinforced with cartilage rings to prevent the trachea from collapsing and to keep the airway patent despite the pressure changes that occur during breathing. The advantage of the rings not being complete posteriorly is that the esophagus is allowed to expand anteriorly during swallowing.

Iam not sure but to me it with be a or dsorry if i was late! hope this ! : )if you really want me to find out the answer that is correct tell me and i will do more research but the a or d makes sense to me.