Answer:
D) A thing or event that causes a reaction.
Explanation:
C is the awnser i hope this helped >_<
The answer is number 2. A will pair with T and C will pair with G
Lungs, nose, airway, mouth, pharynx, larynx,trachea,bronchi, and bronchioles. Its three of those but thats all i could think of from the top of my head. Good luck
Endocrine system is involved in this