填空题
下面程序是由鼠标事件在窗体上画图，如果按下鼠标将可以画图，双击窗体可以清除所画图形。补充完整下面的程序。
首先在窗体层定义如下变量：
Dim PaintStart As Boolean
编写如下事件过程：
Private Sub Form_Load()
DrawWidth=2
ForeColor=vbGreen
End Sub
Private Sub Form_MouseDown(Button As Integer，Shift As Integer，_
X As Single，Y As Single)
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End Sub
Private Sub Form_MouseMove(Button As Integer，Shift As Integer，_
X As Single，Y As Single)
If PaintStart Then
PSet(X，Y)
End If
End Sub
Private Sub Form_MouseUp(Button As Integer，Shift As Integer，_
X As Single，Y As Single)
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End Sub
Private Sub Form_Db1Click()
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End Sub