hi problem in the selection screen

here is my query......

SELECT-OPTIONS: bldat FOR bkpf-budat MODIF ID grp1,

monat FOR bkpf-monat MODIF ID grp2,

gjahr FOR bkpf-gjahr MODIF ID grp2,

xblnr FOR bkpf-xblnr,

kunnr FOR bseg-kunnr,

frmty FOR j_1ifrdtso-j_1ifrmtyp.

when i put the cursor in the field "budat" i.e grp1 then the fields which r under the grp2 should be disabled and viceversa

awaiting for u r reply