The answer for this question would be choice "B. The average annual dose of background radiation is 250 times smaller than the dose linked to increased cancer risk."
You only have to compare 4.0 x 10^-4 and 1.0 x 10^-1. And if you can observe carefully, when you try to multiply the average annual dose of background radiation by 250, you would get 0.1 which is equivalent to the amount of annual dose linked to increased cancer risk. Therefore, the answer is B.