Let D denote that the fetus has a genetic marker for Down syndrome and N denote that ultrasound test is normal. 1 out of 80 fetuses have the genetic marker for Down syndrome. Half of those with genetic marker has a test normal. All of those without genetic marker have test normal. What is the probability if randomly selected fetus has the ultrasound test not normal will not have the genetic marker for Down syndrome? Select one: O a. 0 O b. 1 O c. 1/159 O d. 1/160