Which school has an enrollment of A and had lost river as their previous conference?
CREATE TABLE "membership" (
  "school" text,
  "location" text,
  "mascot" text,
  "county" real,
  "enrollment" text,
  "ihsaa_class" text,
  "year_joined" real,
  "previous_conference" text
);
SELECT "school" FROM "membership" WHERE "previous_conference"='lost river' AND "enrollment"='a';