Which country's material was concrete when the span metres were less than 270, span feet is more than 837, and the year opened was 1943?
CREATE TABLE "completed_bridges" (
  "rank" real,
  "name" text,
  "span_metres" real,
  "span_feet" real,
  "material" text,
  "year_opened" text,
  "country" text
);
SELECT "country" FROM "completed_bridges" WHERE "material"='concrete' AND "span_metres"<270 AND "span_feet">837 AND "year_opened"='1943';