1. (2019高三下·浙江月考) 本程序的功能是在列表框List1中随机产生n(n为偶数)个[1,20]之间的不重复正整数，存入数组a中。点击“排序”按钮Command1，对n个数进行排序。使得奇数位上是降序，偶数位上是升序，且a(1)<a(2)，并在List2中显示排序后的结果。实现该功能的VB程序如下，但加框处代码有错，请改正。

Const n = 8

Dim a(1 To n) As Integer, b(1 To n) As Integer

Private Sub Form_Load()

    ‘随机产生n个[1,20]之间的不重复的正整数，并在list1中显示，具体代码略

End Sub

Private Sub Command1_Click()

    Dim i As Integer, j As Integer, t As Integer, p as integer, p as integer

    For i = 1 To n - 1

        For j = n To i + 1 Step -1

            If a(j) < a(j - 1) Then

                t = a(j)：a(j) = a(j - 1)： a(j - 1) = t

            End If

        Next j

    Next i

    p = n:    ‘①

    For i = 1 To n Step 2

            ‘②

        b(i + 1) = a(q)

        p = p - 2

        q = q + 1

    Next i

    For i = 1 To n

        List2.AddItem Str(b(i))

    Next i

End Sub

① ②