user: Question: During what Championship was the Opponent Jeff Borowiak?
Columns: ['Outcome', 'Date', 'Championship', 'Surface', 'Opponent', 'Score']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1971.0, 'Merion , U.S.', 'Hard', 'Clark Graebner', '2–6, 4–6, 7–6, 5–7']
SQL:

assistant: SELECT "Championship" FROM "Table" WHERE "Opponent" = 'Jeff Borowiak';