Which of the Following Best Defines the Term 'Frequency

Which of the following best defines the term 'frequency'?

A) The number of people exposed to the message.
B) The average number of times someone is exposed.
C) The ability to draw repeat visits and to keep people.
D) A comparison of how well different creative executions generate a response.
E) The number of people exposed to an online ad who actually select to see it.