The lower respiratory system utilizes a number of different mechanisms that confer protection and ...

The lower respiratory system utilizes a number of different mechanisms that confer protection and maintain homeostasis. Which of the following physiological processes protects the lower respiratory system?
 
  A) Goblet cells throughout the lower airways produce phagocytes that trap particles and microorganisms.
  B) The carina, where the trachea bifurcates into two bronchi, closes off the lower airway in response to noxious stimuli.
  C) The alveoli produce positive pressure in order to expel particles that have been inhaled.
  D) Cilia sweep foreign material and mucus upward toward the trachea and larynx where they can then be swallowed.