Final answer:
Increased nasal secretions and abdominal pain are the symptoms of Barb's allergy that are most likely to be resolved following administration of an antihistamine.
Step-by-step explanation:
Barb's symptoms that are MOST LIKELY to be resolved following administration of an antihistamine are increased nasal secretions and abdominal pain.
Antihistamines are drugs that reduce or eliminate the effects of histamines, which trigger the inflammatory response in allergies. Increased nasal secretions and abdominal pain are common symptoms of an allergic reaction, and antihistamines can help alleviate these symptoms by preventing mast cells from releasing histamines.
Therefore, the correct answer is B) Increased nasal secretions and abdominal pain.