Which Previous conference has a Year joined smaller than 1976, and an IHSAA Class of A?
CREATE TABLE "membership" (
  "school" text,
  "location" text,
  "mascot" text,
  "enrollment" real,
  "ihsaa_class" text,
  "num_county" text,
  "year_joined" real,
  "previous_conference" text
);
SELECT "previous_conference" FROM "membership" WHERE "year_joined"<1976 AND "ihsaa_class"='a';