What is the primary conference with a IHSAA Football Class of A, at South Decatur school?
CREATE TABLE "indiana_high_school_athletics_conference" (
  "school" text,
  "location" text,
  "mascot" text,
  "enrollment" real,
  "ihsaa_football_class" text,
  "primary_conference" text,
  "county" text
);
SELECT "primary_conference" FROM "indiana_high_school_athletics_conference" WHERE "ihsaa_football_class"='a' AND "school"='south decatur';