give me the race class with the most number of races
select class from race group by class order by count ( * ) desc limit 1
on what date is it?
select date from race where class = ( select class from race group by class order by count ( * ) desc limit 1 )
list the race id
select race_id from race where class = ( select class from race group by class order by count ( * ) desc limit 1 )