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_68 (year INTEGER, position VARCHAR, class VARCHAR, stages_won VARCHAR)
### Question:
What is the average year that has a car that won 0 stages with a position of DNF?
### Answer:
SELECT AVG(year) FROM table_name_68 WHERE class = "car" AND stages_won = "0" AND position = "dnf"