Which class has a year prior to 2011 and audi r15 tdi as the chassis?
CREATE TABLE "complete_american_le_mans_series_results" (
  "year" real,
  "entrant" text,
  "class" text,
  "chassis" text,
  "engine" text,
  "rank" text,
  "points" text
);
SELECT "class" FROM "complete_american_le_mans_series_results" WHERE "year"<2011 AND "chassis"='audi r15 tdi';