selection screen default value maintain,user cant chage the default value

hi Friends

SELECTION-SCREEN BEGIN OF BLOCK SCLDBLOCK WITH FRAME.

SELECT-OPTIONS: S_WERKS FOR EBAN-WERKS DEFAULT 'IN01' NO INTERVALS NO-EXTENSION ,

S_MATNR FOR EBAN-MATNR,

S_BANFN FOR EBAN-BANFN,

S_EBELN FOR EBAN-EBELN,

S_LIFNR FOR EBAN-LIFNR,

S_BSART FOR EKKO-BSART DEFAULT 'IN03' OBLIGATORY NO INTERVALS NO-EXTENSION,

S_EINDT FOR EKET-EINDT OBLIGATORY.

SELECTION-SCREEN END OF BLOCK SCLDBLOCK.

here i need to maintain bsart in03 ,user cant able to chage anything instead of in03.what can i do for that one

Regards

ds