When riding in rain, why should a motorcyclist avoid accelerating or braking over manhole covers (tapas de alcantarilla) and metal expansion joints (juntas de dilatación)?

1. Because metal becomes magnetized and attracts the motorcycle frame
2. Because wet smooth metal has virtually zero friction, causing sudden wheel spin, loss of traction, and low-side crashes
3. Because it causes the spark plugs to short out
4. Because metal surfaces heat the tires excessively