user: Question: which Surface has Opponents in the final of Mark Edmondson Sherwood Stewart, and a Tournament of Dallas , U.S.?
Columns: ['Outcome', 'Date', 'Tournament', 'Surface', 'Partner', 'Opponents in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1976.0, 'La Costa , U.S.', 'Hard', 'Gene Mayer', 'Marty Riessen Roscoe Tanner', '6–7, 6–7']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponents in the final" = 'Mark Edmondson Sherwood Stewart' AND "Tournament" = 'Dallas , U.S.';