user: Question: What is the surface made of if the opponent in the final is Hewitt McMillan?
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Partner', 'Opponents in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1978.0, 'Wimbledon', 'Grass', 'Fleming', 'Hewitt McMillan', '1–6, 4–6, 2–6']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponents in the final" = 'Hewitt McMillan';