user: Question: Which has a Score of 6–1, 3–0 Ret.?
Columns: ['Date', 'Tournament', 'Surface', 'Opponent in the final', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['4 February 2002', 'Nottingham , Great Britain F1', 'Carpet', 'Luke Milligan', '6–7(5), 7–6(6), 6–4']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Score" = '6–1, 3–0 Ret.';