题干
小李想用vb制作一个分钟倒计时器，界面如图所示。先在文本框text1中输入分钟数，然后在文本框text2中输入秒钟数，再点击“开始倒计时”按钮开始倒计时。Vb程序如下：
Private Sub Command1_Click()
Timer1.Enabled = ①
End Sub
Private Sub Timer1_Timer()
sec = Val(Text2.Text)
min = Val(Text1.Text)
If sec> 0 Then
sec = sec - 1
Else
sec = 59
If min > 0 Then
min = min - 1
Else
Text1 = 0
Text2 = 0
MsgBox "倒计时时间到"
End If
End If
Text1 = min
Text2 = sec
End Sub