WHAT WAS THE SURFACE MADE OF WHEN THE OPPONENT WAS GEORGE KHRIKADZE?
CREATE TABLE "singles_7" (
  "edition" text,
  "round" text,
  "date" text,
  "against" text,
  "surface" text,
  "opponent" text,
  "w_l" text,
  "result" text
);
SELECT "surface" FROM "singles_7" WHERE "opponent"='George Khrikadze';