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_88 (nation VARCHAR, world_rank VARCHAR, birth_date VARCHAR)
### Question:
what is the nation when the world rank is 6 and the birth date is 1971-07-31?
### Answer:
SELECT nation FROM table_name_88 WHERE world_rank = "6" AND birth_date = "1971-07-31"