select n.activity_date,n.advertiser_id,c.type as type from a JOIN b as n -- because of the alias name you've got to reference table b as n -- and you've omitted the AND operator on (a.id=n.id AND a.name=n.name)
JOIN c on n.c_id=c.id where n.country='CA' -- you've got to use n instead of b limit 10;