I believe the answer is A. allergic reaction. Allergic reactions are not nervous system emergency. Examples of nervous system emergencies include seizures, stroke
Seizures is a temporary alteration in behavior due to the massive electrical discharge of one or more groups of neurons in the brain. Stroke on the other hand is caused by either ischemic or hemorrhagic lesions to a portion of the brain, resulting in damage or destruction of brain tissue. A heart attack develops when blood flow is blocked and a segment of the heart muscle/tissue dies or is damaged.