Q: When does a default Analytics session expire?
A) When a user opens another browser window
B) At noon every day
C) When a user is inactive on your website for more than 30 minutes
D) After 30 minutes, regardless of user activity on your website
Correct Answer is C) When a user is inactive on your website for more than 30 minutes
Sessions and campaigns end after a specific amount of time passes. By default, sessions end after 30 minutes of inactivity and campaigns end after six months. You can change the settings so sessions and campaigns end after the specified amount of time has passed.
Learn more here: https://support.google.com/analytics/answer/2795871