下面程序运行时，单击窗体后，窗体上显示的结果是( )。 Private Sub Form_Click Dim I As Integer Dim sum As Long Dim t1 As Long t1=1:sum=0 For 1=1 To 3 t1=t1*I sum=sum+t1 Next I Print sum End Sub

A．3

B．9

C．5

D．6