Table: circuit_nations_races
Columns: date
race
race_track
category
lap_length

Question: What is the Lap Length of the race with a Grand Prix Fia Category?
SQL: SELECT "lap_length" FROM circuit_nations_races WHERE "category" = 'grand prix fia'

Question: What is the Race on July 30, 1950 with a Formula 2 Fia, non-championship?
SQL: SELECT "race" FROM circuit_nations_races WHERE "category" = 'formula 2 fia, non-championship' AND "date" = 'july 30, 1950'