Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_57 (tournament VARCHAR)
### Question:
Which 1997's accompanying 1991 was a when the tournament was the australian open?
### Answer:
SELECT 1997 FROM table_name_57 WHERE 1991 = "a" AND tournament = "australian open"