The correct answer is A. Certificate or diploma
Step-by-step explanation:
One of the main ways to know if a health care professional is legitimately qualified is through certificate, diplomas or similar documents because these prove the professional participated in educational programs that train appropriately health care professionals. Also, a diploma or certificate in specific areas shows the professional has knowledge and experience to provide treatment for certain conditions, give recommendations to patients, etc.
On the other hand, that a professional promises a cure, offers a secret cure or does not talk about qualifications might be an indicator that he or she is not qualified as these are non-professional behaviors. Therefore, the one that can help identify a legitimately qualified health care professional is a certificate or diploma.