新手做的报价系统，出现“请输入参数”看了论坛的解决帖子认不得

Private Sub Allfilter()
Dim str As String

If IsNull(Me.规格a.Value) = False Then
    str = str & " and 规格a='" & Me.规格a.Value & "'"
End If
If IsNull(Me.规格b.Value) = False Then
    str = str & " and 规格b='" & Me.规格b.Value & "'"
End If
If IsNull(Me.规格c.Value) = False Then
    str = str & " and 规格c='" & Me.规格c.Value & "'"
End If
If IsNull(Me.规格d.Value) = False Then
    str = str & " and 规格d='" & Me.规格d.Value & "'"
End If

str = "True"
Me.Filter = str
Me.FilterOn = True
Me.报价 = 售价

End Sub

红色的地方有问题