user: Question: When was the 1991 World Group I with the opponent of Li Fang?
Columns: ['Edition', 'Round', 'Date', 'Surface', 'Opponent', 'Result']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1983 World Group I', 'R1', 'July 17, 1983', 'Clay', 'Christiane Jolissaint', '4–6, 6–4, 4–6']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Edition" = '1991 World Group I' AND "Opponent" = 'Li Fang';