M=["l","2","4","3"]

M.sort( )

print( M)

n= 5

head=0

tail=4

que=['a' , 'b' ,'c' ,'d' ,'e' ]

while head!=tail:

    if head%4==0:

        print (que[head])

    else:

        tail=(tail+1)%n

        que[tail]=que[head]

    head= (head+1)%n

print (que[head])

q=[""]*50

head=tail=0

s="ningbo'

for i in s:

    q[tail]=i

    tail+=1

while head<tail:

    print(q[head],end="")

    head+=1

    for i in range(3):

        q[tail]=q[head]

        head+=1

        tail+=1

执行该程序段后，输出结果为（   ）