 Hi and welcome to the session. I'm Shashri and I'm going to help you with the following question. Question says, choose the correct answer in each of the following. If A and B are two events such that probability of A is not equal to 0 and probability of B when A has occurred is equal to 1, then we have to choose the correct answer from A, B, C and D. Let us now start with the solution. Now we have given probability of B when A has occurred is equal to 1. You also know that probability of B when A has occurred is equal to probability of B intersection A upon probability of A. You know this is the conditional probability and according to conditional probability probability of event B when A has occurred is equal to probability of B intersection A upon probability of A where probability of A is not equal to 0. Now we are given in the question that probability of A is not equal to 0. Clearly we can see here. Now we can write probability of B when A has occurred is equal to 1 implies that probability of B intersection A upon probability of A is equal to 1. Clearly we can see we can substitute this value for this probability. So here we have written this value for this probability in this expression. Now we are replying both the sides of this expression by probability of A we get probability of B intersection A is equal to probability of A. Now we know probability of B intersection A is equal to probability of A only when B intersection A is equal to A. So we can write probability of B intersection A is equal to probability of A implies B intersection A is equal to A. Now this further implies A is a subset of B. So our correct answer is A. So this is our required answer. This completes the session. Hope you understood the solution. Take care and have a nice day.