user: Question: What is the surface of the tournament with a Runner-up outcome and Dudi Sela as the opponent?
Columns: ['Outcome', 'Date', 'Tournament', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Winner', '28 March 2005', 'Grasse , France', 'Clay', 'Stefan Wauters', '6–2, 6–3']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Outcome" = 'Runner-up' AND "Opponent" = 'Dudi Sela';