子窗体中定义的变量如何在父窗体中也能使用？

lyia

子窗体中的代码：
Option Compare Database
Option Explicit
Public strThcd, strBbcd As Variant
Private Sub 版本_AfterUpdate()

    strBbcd = Me.版本.Value
    Debug.Print "sub" & strThcd
    Debug.Print "sub" & strSjcd
End Sub

Private Sub 图号_AfterUpdate()
    strThcd = Me.图号.Value
End Sub

父窗体：
Option Compare Database
Option Explicit
Public strSjcd As Variant
Private Sub Combo4_AfterUpdate()

    strSjcd = Me.Combo4.Value
   
End Sub

Private Sub Command6_Click()
    DoCmd.SetWarnings True
    Debug.Print "z" & strSjcd
    Debug.Print "z" & strThcd
    Debug.Print "z" & strBbcd
    DoCmd.RunSQL "INSERT INTO 零件补充信息表(图号,版本,设计员ID) VALUES(strThcd,strBbcd,strSjcd)"
End Sub