How would you achieve this?

You want a record of all queries that are not using indexes.
How would you achieve this?

A.
By enabling the Slow Query Log because all queries that are not using indexes will be logged
automatically

B.
By enabling the Error Log because not using indexes is an error

C.
By enabling the Slow Query Log and using the – log-queries-not-using-indexes option

D.
By enabling the Error Log and using the – log-queries-not-using-indexes option

Explanation:
Reference: http://dev.mysql.com/doc/refman/5.0/en/slow-query-log.html