Final answer:
The APA is a professional association for clinical and research psychologists in the United States, focusing on promoting and disseminating psychological knowledge.
Step-by-step explanation:
The American Psychological Association (APA) is a professional association in the United States for clinical and research psychologists. Essentially, it is the largest organization of psychologists in the world with a mission to promote and disseminate psychological knowledge. The APA has various functions, including holding conferences, accrediting university degree programs, and publishing scientific journals. There are many divisions within the APA that cater to numerous specialties in psychology, thus showcasing the diversity within the field. Given this information, the correct answer to the multiple-choice question, 'What is the APA?' is c. A professional association in the United States for clinical and research psychologists.