Which of the Following Best Describes the Concept of Marginal

Which of the following best describes the concept of marginal probability?

A) It is a measure of the likelihood that a particular event will occur,regardless of whether another event occurs.
B) It is a measure of the likelihood that a particular event will occur,given that another event has already occurred.
C) It is a measure of the likelihood of the simultaneous occurrence of two or more events.
D) None of the above.