A class has 4 freshmen and 6 sophomores. An exam is given and the students are ranked according to their scores. Assume that no two students have the same score. (a) How many different rankings are there? (b) If all possible rankings are equally likely, what is the probability that two of the students, Alice and Bob, are not adjacent in the ranking? (c) If all possible rankings are equally likely, what is the probability that the first of the ranking or the last of the ranking (or both) is a sophomore?