While Jessica, Ashley, and Bryan are snowboarding, they ignore warning signs indicating that they have left the marked trail and are entering dangerous territory. They become lost, and a rescue effort begins. Climbing the mountain, a snowplow accidentally cuts a nearby town's main electrical cable. Due to the loss of her electric heat, Ethel, an elderly woman, dies of hypothermia. The boarders' negligence in ignoring the warning signs is
d. the causation in fact, but not the proximate cause, of Ethel's death.