The Centers for Disease Control and Prevention (CDC) is recognized as the lead United Statesagency[?] for protecting the health and safety of people by providing credible information to enhance health decisions, and promoting health through strong partnerships. CDC serves as a national focus for developing and applying disease prevention and control (especially infectious diseases), environmental health[?], and health promotion[?] and education[?] activities designed to improve the health of the people of the United States.
... "either of those element(s) of the field whose square equals b2 - 4ac". In some fields, some elements have no square roots and some have two; only zero has just one square ...