Your doctor has given you a patient memo that he has written. You notice that his grammar and punctuation need corrected. Which of the following proofreader's marks signifies that a period is to be introduced into a sentence?

The three most common certifications for Medical Assistants in United States are offered by the American Association of Medical Assistants (AAMA), the American Medical Technologists (AMT) and the National Center for Competency Testing (NCCT). These exams mainly cover the following three subject areas: General Knowledge, Administrative Knowledge and Clinical Knowledge.