Private Sub Command1 Click()

Dim a As Integer, b As Integer

a = 5: b = 8

b = a + b

label1.Caption = Str(b)

End Sub

引发此错误的语句可能为（   ）

Dim a(1 To 5) As Integer, i As  Integer

a(1)=1: a(2)=1

For i=3 To  5

a(i)=a(i-1)+a(i-2)

Next i

Text1.Text=Str(a(i-1))

该程序段运行后，文本框Textl中显示的内容是（  ）

Dim n As Integer，s As String

n = 64 :s = ""

Do While n > 0

  s = Str(n Mod 7) + s

  n = n \ 7

Loop

执行该程序段后，变量s的值是（  ）

Private Sub Command1_Click()

Dim u As Single, x As Single, y As Single, z As Single

u=Val(Text1.Text)

x=(u+10)/(u*u+8)

y=(u-1)/(x+u)

z=Sqr(x-y)

Text2.Text=Str(z)

End Sub

程序运行时，在文本框Text1中输入-1，单击命令按钮Command1，弹出如图所示的错误提示信息。产生此错误的语句是（  ）