The API changes should provide both source and binary（ ）for programs written to the  original API.That is, existing program binaries should continue to operate when run on a system  supporting  the  new  API.In  addition,  existing（_______）that  are  re-compiled  and  run  on  a   system  supporting the new API should continue to operate.Simply put, the AP（   ） for multicast receivers that specify source filters should not break existing programs.The changes to the API should be as small as possible in order to simplicity the task of converting existing（ ） receiver applications to use  source  filters.  Applications  should  be  able  to  delete  when  the  new（ ） filter  APIs are  unavailable(e.g., calls fail with the ENOTSUPP error) and react gracefully(e.g., revert to old non-source-filter API or display a meaningful error message to the user).

横线处应选（   ）。