1. (2020高三下·金华月考) 有VB程序段如下：

s = "2019appreciate": sum = 0

For i = 1 To Len(s)

  ch = Mid(s, i, 1)

  If ch >= "a" And ch <= "z" Then

    m = Asc(ch) - Asc("a") + 1

    a(m) = a(m) + 1

  End If

 Next i

 For i = 1 To 10

  If a(i) > 0 Then sum = sum + 1

 Next i

数组a各元素的初始值都为0，执行该程序段后，变量sum的值为（  ）