What is the average year that has a car that won 0 stages with a position of DNF?
CREATE TABLE table_name_68 (
    year INTEGER,
    position VARCHAR,
    class VARCHAR,
    stages_won VARCHAR
)
SELECT AVG(year) FROM table_name_68 WHERE class = "car" AND stages_won = "0" AND position = "dnf"
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What is the average year that has a car that won 0 stages with a position of DNF? ### Input: CREATE TABLE table_name_68 (
    year INTEGER,
    position VARCHAR,
    class VARCHAR,
    stages_won VARCHAR
) ### Response: SELECT AVG(year) FROM table_name_68 WHERE class = "car" AND stages_won = "0" AND position = "dnf"