What is the listing for the US Open in 1977?
CREATE TABLE "grand_slam_success" (
  "tournament" text,
  "1968" text,
  "1969" text,
  "1970" text,
  "1971" text,
  "1972" text,
  "1973" text,
  "1974" text,
  "1975" text,
  "1976" text,
  "1977" text,
  "1978" text,
  "1979" text,
  "career_sr" text,
  "career_w_l" text,
  "career_win_pct" text
);
SELECT "1977" FROM "grand_slam_success" WHERE "tournament"='us open';