vba工程提示时间

Private Declare Function Beep Lib "kernel32" (ByVal dwFreq As Long, ByVal dwDuration As Long) As Long
Sub bb()
t = Timer
If [a1].Value = 5 Then
UserForm1.Show 0
Application.OnTime Now + TimeSerial(0, 0, 1), "bb"

[a1] = [a1] - 1
Beep 800, 50

ElseIf [a1].Value = 0 Then
Beep 1000, 100
MsgBox "时间到！"
Unload UserForm1
Else
Application.OnTime Now + TimeSerial(0, 0, 1), "bb"
[a1] = [a1] - 1
Beep 800, 50
End If
End Sub

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如果用VBA代码播放WAV声音文件，可以用下面的代码： 
    Private Declare Function sndPlaySound32 _
    Lib "winmm.dll" _
    Alias "sndPlaySoundA" ( _
        ByVal lpszSoundName As String, _
        ByVal uFlags As Long) As Long