user: Question: Name the year for Clay for Boston and Guillermo Vilas
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Opponent in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1973.0, 'Monte-Carlo', 'Clay', 'Ilie Năstase', '4–6, 1–6, 2–6']
SQL:

assistant: SELECT "Year" FROM "Table" WHERE "Surface" = 'Clay' AND "Championship" = 'Boston' AND "Opponent in the final" = 'Guillermo Vilas';