Note that the product of slopes of two perpendicular lines is equal to -1 (and the slopes of two parallel lines are equal). Note also that the angle in a semicircle is 90 degrees.
Statement 1: product of slopes = -1, hence, AB is perpendicular to BC and B is a right angle. Which means AC is a diameter such that ABC form a semi-circle.
Statement 2: I am not sure about this part. AB = 12 and BC = 5 does not necessirily mean AC = 13 (implying a right triangle). Hence, I am not sure whether statement 2 alone is sufficient.
I will go with Answer A. I might have to think about statement 2 again to be sure.