Answer:
A. first line of defense
Explanation:
The immune system is a set of elements existing in the human body which interact with each other and aim to defend the body against disease, viruses, bacteria, microbes and others. The human immune system serves as a barrier that protects us from unwanted elements (like bacterias, microbes etc), antigens, that try to invade our body. So, it represents the defense of the human body. The body's defense process through the immune system is called the immune response and there are 2 types of immune responses: innate, natural or non-specific and acquired, adaptive or specific.
Innate or natural immunity is our first line of defense. This type of immunity is already born with the person, represented by physical, chemical and biological barriers. This is case of Larry, which the pollen (antigen) got in contact with the barrier of Larry's body, which is the mucus: a fluid produced by the body that has the function of preventing microorganisms from entering the respiratory system.