Question: What was the surface for Adrian Ungur as an opponent?
SQL: SELECT "Surface" FROM "2-13900387-2" WHERE "Opponent" = 'Adrian Ungur';

Question: What was the score on a Clay surface on May 29, 2006?
SQL: SELECT "Score" FROM "2-13900387-2" WHERE "Surface" = 'Clay' AND "Date" = 'May 29, 2006';

Question: Which tournament had a score of 6–3, 7–6?
SQL: SELECT "Tournament" FROM "2-13900387-2" WHERE "Score" = '6–3, 7–6';

Question: On what surface was the opponent Michael Berrer?
SQL: SELECT "Surface" FROM "2-13900387-2" WHERE "Opponent" = 'Michael Berrer';