请问为何 Set rs =nothing 不生效

要在ACCSEE窗体上实现一个省份和城市的级联下拉框，在省份框的更新后事件里写的如下代码：

Private Sub province_AfterUpdate()
Dim strWhere
Dim strWhere2
Dim strSql
Dim var
Dim rs As Recordset
Dim rs2 As Recordset

strWhere = Null
strWhere2 = Null
'Set rs = Nothing
'Set rs2 = Nothing
'Set rs = Nothing
 
If Not IsNull(Me.province) Then

If Not IsNull(strWhere2) Then
strWhere2 = strWhere2 & "AND ([pname] like '" & Me.province & "')"
Else
strWhere2 = strWhere2 & "([pname] like '" & Me.province & "')"
End If

End If

Set rs = CurrentDb.OpenRecordset("select * from t_zd_province where " & strWhere2)

If Not IsNull(rs) Then
var = rs("pid")
If Not IsNull(strWhere) Then
strWhere = strWhere & "AND ([sprovinceid] like '" & var & "')"
Else
strWhere = strWhere & "([sprovinceid] like '" & var & "')"
End If

End If

'MsgBox (strWhere)
    rs.close

Set rs = Nothing

Set rs2 = CurrentDb.OpenRecordset("select * from t_zd_city where" & strWhere)

If Not rs2.EOF Then
        rs2.MoveFirst
       
        Do While Not rs2.EOF
            
           Me.city.AddItem (rs2("cname"))
            rs2.MoveNext
        Loop
       
    End If
   
rs2.close
Set rs2 = Nothing

End Sub

但每次更换省份后，上一次的城市还在里面，就形成了累计，也就是我的rs2没有清空，请问各位大侠，什么原因呢？