Answer:
A. bounce rate
Explanation:
A bounce on your page is a one-page session.
In Analytics, a bounce is explicitly defined as a request that causes only one query to the Analytics server, for example when a visitor loads a single page on your website and then exits the Analytics database during that session without triggering any other queries.
Bounce rate is one-page sessions separated by all sessions, or the percentage of all sessions on your site where users only viewed one page and only triggered a single request to the Analytics server.
These one-page visits have a session period of 0 seconds because after the first one there are no additional hits that would allow Analytics to measure the time.