1. (2023·浙江模拟) 有如下Python程序段，运行后程序的输出结果是（   ）

a = [[3,1], [2,2], [3,3], [3,4], [17,5], [2,6], [3,-1]]

p = head = 0

while p != -1:

    q = p

    while q != -1:

        t = q

        q = a[q][1]

        if q != -1 and a[q][0] == a[p][0]:

            a[t][1] = a[q][1]

            q = t

    p = a[p][1]

p = head

while p != -1:

    print(a[p][0], end=' ')

    p = a[p][1]