What countries are visited in the episode presented by Brian B. Thompson?
CREATE TABLE "table1_15211468_1" (
  "episode_no" text,
  "episode_title" text,
  "uk_broadcast_date" text,
  "presenter" text,
  "details_of_journey" text,
  "countries_visited" text
);
SELECT "countries_visited" FROM "table1_15211468_1" WHERE "presenter"='Brian B. Thompson';