Answer:
Competence
Explanation:
Credibility generally has three different types of elements or factors, and includes, competence, compassion, and confidence.
Hence, in this case, when the speaker mentions that she is the head of neurology at a major medical center, she is trying to let the audience understand or know that she is competent or has competency in telling them the dangers involved in not wearing helmets for bicyclists of all ages.
Therefore, the correct answer is COMPETENCE.