Add check box before each line

Hi All,

I am using alv grid to print the out put. It is comming correct. I want to add check box before each line of out put. How can I do it?

And in the selection screen I want delivery block p_lifsk as '01' fixed, so that user cannot change the value.

Please help me.

Thanks

Veni.

PERFORM get_data.
  PERFORM PROCESS_data.
  perform sub_alv_routines.
  perform comment_build  using t_list_top_of_page[].
  g_repid = sy-repid.
  perform alv_build_fieldcat using 'IT_OUTPUT' g_repid.
  perform sub_call_alv_grid tables it_output.