Answer:
A. The probability of event B occurring, given that event A has occurred
Explanation:
Conditional probability
A probability is conditional if is depends on what has already happened.
The probability that event B happens, given that event A has already happened is "B given A" or P(B | A)
Therefore, P(B | A) means "The probability of event B occurring, given that event A has occurred"
Additional information:
P(A | B) means "A given B", i.e. the probability of event A occurring, given that event B has occurred
P(A ∩ B) means the probability of event A and event B both happening.