What is the primary hazard of riding with loose, flapping clothing (such as unzipped jackets or long scarves)?

1. It causes the motorcycle exhaust to backfire
2. Loose garments can whip painfully against the rider, snag on passing objects, or become entangled in the rear wheel and chain sprockets
3. It makes the speedometer read 20 km/h slower
4. It causes engine spark plugs to foul