NOTE. IF SOMEONE THINKS LIKE FOLLOWING WAYS, THEN HE/SHE IS LACKING CONCEPT OF PROBABILITY.
BY FOLLOWING WAYS, ANSWER IS CORRECT, BUT METHOD IS ABSOLUTELY WRONG.
We know from set theory A INTERSECTION B = A-(A-B)
Here, SET B CONTAINS MORE ELEMENT THAN SET A as P(B)=1 and P(A)=0.5
Therefore, A INTERSECTION B = B-(B-A) = 1-(1-0.5)= 1-0.5= 0.5
now, substituting value of A INTERSECTION B in respective equations we can get the answers. using
P(B/A)= P(A INTERSECTION B)/P(A) as A INTERSECTION B = B INTERSECTION A ( from set theory property)
Hence, option C is the correct option.