Table: murder_she_wrote_tv
Columns: season
episodes
season_premiere
season_finale
tv_season
rank
households_millions

Question: WHAT SEASON HAD A SEASON FINALE OF MAY 21, 1989 AND WAS VIEWED BY 17.98 MILLION HOUSEHOLDS?
SQL: SELECT MAX("season") FROM murder_she_wrote_tv WHERE "season_finale" = 'may 21, 1989' AND "households_millions" < 17.98