The total probability rule is used when an an analyst is interested in a)all potential outcomes. So, correct option is a.
Probability is the branch of the mathematics concerning numerical descriptions of how likely an event is going to occur, or how likely it is that a proposition is true. The probability of an event is the number between 0 and 1, where, roughly speaking, 0 indicates that impossibility of the event and 1 indicates certainty. If probability of an event is higher then, the more likely it is that the event will occur.
Probability can be defined as the proportion of the number of favorable outcomes to the total number of outcomes of an event..
Hence, option a is correct.
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