A.S->top==0 B.S->top!=0 C.S->top==n D.S->top!=n
A.3,4,5,1,2 B.2,4,1,3,5 C.3,5,4,2,1 D.1,3,5,2,4
A.棧底 B.棧頂 C.任意位置 D.指定位置