error "only one expression can be specified in the select list wwhen the subquery is not introduced with EXISTS"

i am getting this error message "only one expression can be specified in the select list wwhen the subquery is not introduced with EXISTS" when i run this query
SELECT DISTINCT                          a.transport, a.office, a.importer_cod, a.entry_date, a.dec_cargo_type, d.val_asgn_date, e.val_reg_date, e.val_reg_reldate, e.val_outdate, e.doc_indate,                          f.dec_reg_date, f.sad_reg_date, f.dec_rel_date, f.dec_exam_indate, f.dec_exam_outdate, f.dec_audit_indate, f.dec_audit_outdate, f.dec_rec_indate,                          f.dec_exam_mayB_date, f.assmt_notice_date, ...