user: Question: When was Varvara Lepchenko the opponent?
Columns: ['Date', 'Tournament', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['13 August 2007', 'Pesaro , Italy', 'Clay', 'Stephanie Vogt', '6–2, 2–6, 6–1']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Opponent" = 'Varvara Lepchenko';