填空题 运行下面程序，单击Command1，在窗体上显示a的值是 1，b的值是 2，i的值是 3。
Option Explicit
Private Sub Command1_Click()
Dim i As Integer, a As Integer, b As Integer
a=1:b=20
For i=a To b Step a+1
a=a+1
b=b-1
i=i+1
Next i
Print a; b; i
End Sub