Here are the answers to your questions:
Question 1: Which methodology relies heavily on client involvement in setting priorities?
Answer: agile development
Question 2: What is the purpose of the scrum retrospective?
Answer: to analyze the effectiveness and efficiency of the development process and to assess the resources needed by the team
Question 3: What do extreme programming, scrum, and Kanban have in common?
Answer: Each methodology approaches development in short repeated bursts of activity.
Question 4: What is Git?
Answer: a commonly used Version Control System (VCS)
Question 5: What is GitHub?
Answer: a web-hosted version of a Version Control System (VCS) using Git