Which wheel arrangement had a Specification of dl-700?
CREATE TABLE "rs_series_b_b" (
  "model" text,
  "specification" text,
  "build_date" text,
  "total_produced" real,
  "wheel_arrangement" text,
  "prime_mover" text,
  "power_output" text
);
SELECT "wheel_arrangement" FROM "rs_series_b_b" WHERE "specification"='dl-700';