根据算法将下列程序补充完整。

Private Sub Command1_Click()

  Dim S As String，ch As String

  Dim ch2 AS String，sum As Double

  Dim n As Integer，i As Integer

  s=Text1．Text

    ①  

  i=1：sum=0

  Do While i<=n

      ch=Mid(s，i，1)

      If ch>=“0”And ch<=“9”Then

        j=i

        ch2=Mid(s，j，1)

        Do While ch2>=“0”And ch2<=“9”

          j=j+1

         ch2=Mid(s，j，1)

        Loop

       sum=sum+    ②   

       i=j

      EndIf

      i=i+1

  Loop

    Label3．Caption=Str(sum)

End Sub

1图

2图

Dim c As String, i As Integer

Dim s As String, s1 As String

s = "Jishu_Xuankao_2020"

s1 =""

For i = 1 To Len(s) Step 2

  c = Mid(s, i, l)

  If c >= "a" And c <= "z" Then s1=c+s1

Next i

Text1. Text = s1

执行该程序段后，文本框Text1显示的内容是（  ）

DIM A（1991 TO 1998） AS INTEGER

FOR I=1 TO 8

   A(I)=I

PRINT A(I)；

       NEXT I