Stack A has the entries a, b, and c (with a on top). Stack B is empty. An entry popped out of stack A can be printed immediately or pushed to stack B. An entry popped out of stack B can only be printed. In this arrangement, Which of the following permutations of a, b, and c are not possible?
1
b a c
2
c b a
3
c a b
4
a b c