What is the intro date for the throughput of 16 mbit/s?
CREATE TABLE "references" (
  "manufacturer" text,
  "model" text,
  "intro_date" text,
  "interface" text,
  "os" text,
  "price_usd" real,
  "price" text,
  "throughput" text
);
SELECT "intro_date" FROM "references" WHERE "throughput"='16 Mbit/s';