user: Question: Which Margin of victory has a Tournament of U.S. Senior Open?
Columns: ['Date', 'Tournament', 'Winning score', 'Margin of victory', 'Runner(s)-up']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Oct 2, 2011', 'SAS Championship', '−11 (66-69-70=205)', '1 stroke', 'John Huston , Jeff Sluman']
SQL:

assistant: SELECT "Margin of victory" FROM "Table" WHERE "Tournament" = 'U.S. Senior Open';