1. (2015·杭州模拟) 下列VB程序运行时，单击命令按钮Command1后，标签框Label2中显示的内容是

Private Sub Command1_click()

Dim s as integer,I as integer

S=0

For i=1 to 20 step 3

      s=s+(-1)^i*i

Next i

Label1.caption=str(i)

Label2.caption=str(s)

End Sub