单项选择题
窗体上有一个名称为Line1的直线控件,并有如下程序:Dim down As Boolean, x1%, y1%Private Sub Form_Load() Line1.Visible = False down = FalseEnd SubPrivate Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 1 Then down = True x1 = X : y1 = Y End IfEnd SubPrivate Sub Form_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 1 Then down = False Line1.x1 = x1 : Line1.y1 = y1 Line1.x2 = X : Line1.y2 = Y Line1.Visible = True End IfEnd Sub运行程序,按下鼠标左键不放,移动鼠标到窗体其他位置处放开左键,则产生的结果是
A.以鼠标按下和抬起的两点为端点显示一条直线
B.鼠标按下时显示一条直线;鼠标抬起时直线消失
C.直线从鼠标按下处移动到鼠标抬起处
D.鼠标按下时直线消失;鼠标抬起时显示直线