Tell me the D 41 for D 43 of d 18
CREATE TABLE "senate_composition_before_the_elections" (
  "d_41" text,
  "d_42" text,
  "d_43" text,
  "d_44" text,
  "d_45" text,
  "d_46" text,
  "d_47" text,
  "r_53" text,
  "r_52" text,
  "r_51" text
);
SELECT "d_41" FROM "senate_composition_before_the_elections" WHERE "d_43"='d 18';