Question: What time/retired for a grid less than 19, under 21 laps, and made by Aprilia?
SQL: SELECT "Time/Retired" FROM "2-11683537-2" WHERE "Grid" < 19.0 AND "Manufacturer" = 'Aprilia' AND "Laps" < 21.0;

Question: What is the grid for Dirk Heidolf?
SQL: SELECT SUM("Grid") FROM "2-11683537-2" WHERE "Rider" = 'Dirk Heidolf';