Before the Year 1972, what RIAA Sales Certification was awarded to the song that had a Billboard 200 Peak less than 18?
CREATE TABLE "studio_albums" (
  "year" real,
  "title" text,
  "label" text,
  "riaa_sales_certification" text,
  "billboard_200_peak" real
);
SELECT "riaa_sales_certification" FROM "studio_albums" WHERE "billboard_200_peak"<18 AND "year"<1972;