多选题

There is a sequence of n numbers 1, 2, 3,.., n and a stack which can keep m numbers at most. Push the n numbers into the stack following the sequence and pop out randomly.uppose n is 7 and m is 5, please choose the output sequences of the stack.

Question

There is a sequence of n numbers 1, 2, 3,.., n and a stack which can keep m numbers at most. Push the n numbers into the stack following the sequence and pop out randomly. Suppose n is 2 and m is 3, the output sequence may be 1, 2 or 2, 1, so we get 2 different sequences. Suppose n is 7 and m is 5, please choose the output sequences of the stack:

A. 1, 2, 3, 4, 5, 6, 7

B. 7, 6, 5, 4, 3, 2, 1

C. 5, 6, 4, 3, 7, 2, 1

D. 4, 5, 6, 3, 7, 2, 1

E. 1, 7, 6, 5, 4, 3, 2

F. 3, 2, 1, 7, 6,5, 4