Which of the following are true, and which are false? 

a. Bayes nets are organized into layers with connections only between adjacent layers. 

b. The topology of a Bayes net can assert that some variables are not conditionally independent. 

c. Some Bayes nets require as many parameters as the explicitly tabulated full joint distribution. 

d. In any Bayes net, the parents of a single child are always conditionally independent of each other given the child.