填空题

编写计算1/2+2/3+3/4+4/5的程序如下：[把选择题改编成程序填空题]
Private Sub Command1_Click( )
Dim i,n as integer
Dim sum, x as Double
Sum=0
①
For i=1 to 5
②
n=n+1
sum=sum+x
Next i
Text1.text=Str(sum)
End Sub
请在程序画线处填上合适的语句______　　　______