If Request.from("A")="" Or Request.from("B")="" Then
Response.Write "<script language='javascript'>alert(A或B都不能为空,请返回填写。')</script>"
'//注意:用javascript:history.back()进行返回后表单不会被清空。
Response.Write "<script language='javascript'>window.location.href='javascript:history.back()'</script>"
End If