1. (2020高三上·浙江月考) 有如下 VB 程序段：

For i = 1 To 8

    a(i) = Int(Rnd * 7) + 1

Next i

For i = 1 To 3

    For j = 1 To 8 - 2 * i

        If a(j) Mod 7 > a(j + 2) Mod 7 Then

            t = a(j): a(j) = a(j + 2): a(j + 2) = t

        End If 

    Next j

Next i

For i = 1 To 8

    ch(i) = Chr(a(i) + Asc("A") - 1)

Next i

执行该程序段后，ch(1)～ch(8)各元素值不可能的是（   ）