东南丘陵树木比辽东丘陵生长快，主要是因为东南丘陵（　　）

A．土壤肥力高

B．地势海拔高

C．土层深厚

D．热量高、降水多

下面的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_MouscDown(Button As Integer，Shift As Integer，_
X As Single，Y As Single)
[13]
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)
[14]
End Sub
Private Sub Form_DblClick()
[15]
End Sub