que=[""]*20

head,tail= 0,0

for i in range(3):

    que[tail]=chr(97+i)

    tail+= 1

st=["b","c","d","a"]

top=3

while head < tail and top > - 1:

    if st[top]==que[head]:

        head+= 1

    else:

        que[tail] = st[top]

        tail+= 1

    top-= 1

print(que[head:tail])

执行该程序段，则输出的结果是(  )

import random

q=[0]*8 ; head,tail=0,4

for i in range(4):

    k=random.randint(0,10)

    if k%2==0:

        q[tail]=k%5

        tail+=1

    else:

        head+=1

while head<tail:

    print(q[head],end=" ")

    head+=1

程序运行后，输出结果可能为（   ）