user: Question: Name the surfaace where outcome is Runner-up and championship is US Open
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Partner', 'Opponents', 'Score']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Winner', 1990.0, 'US Open', 'Hard', 'Elizabeth Sayers Smylie', 'Jim Pugh Natasha Zvereva', '6–4, 6–2']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Outcome" = 'Runner-up' AND "Championship" = 'US Open';