What team did the Chicago Black Hawks visit on April 20?
CREATE TABLE "montreal_canadiens_4_chicago_black_hawks" (
  "date" text,
  "visitor" text,
  "score" text,
  "home" text,
  "record" text
);
SELECT "home" FROM "montreal_canadiens_4_chicago_black_hawks" WHERE "visitor"='chicago black hawks' AND "date"='april 20';