What is the purpose of a Clean-up Rule?

What is the purpose of a Clean-up Rule?
A . Clean-up Rules do not server any purpose.
B. Provide a metric for determining unnecessary rules.
C. To drop any traffic that is not explicitly allowed.
D. Used to better optimize a policy.

Answer: C

Explanation:

These are basic access control rules we recommend for all Rule Bases:

There is also an implied rule that drops all traffic, but you can use the Cleanup rule to log the traffic.