Final answer:
The internal door handle vent flap improves air circulation inside a vehicle, enhancing comfort and preventing window fogging.
Step-by-step explanation:
The purpose of the internal door handle vent flap is b) To improve air circulation. This feature is often found in vehicles where it allows air to flow into the cabin more effectively. By improving air circulation, it can help to maintain comfort for the passengers, regulate the interior temperature and prevent the windows from fogging up. It is not related to providing additional insulation, blocking drafts, or enhancing security, but is rather focused on maintaining a pleasant and safe driving environment.