Which Surface has a Partner of sorana cîrstea?
CREATE TABLE "doubles_10_2_titles_8_runners_up" (
  "outcome" text,
  "date" text,
  "surface" text,
  "partner" text,
  "opponents" text,
  "score" text
);
SELECT "surface" FROM "doubles_10_2_titles_8_runners_up" WHERE "partner"='sorana cîrstea';