Which of the following is a common cause of wildfires?

Cigarettes and campfires left unattended are widely recognized as common causes of wildfires. This is primarily due to human activity where these items can ignite dry vegetation or other flammable materials in the environment. When not properly extinguished, the heat or burning embers from these sources can result in a fire that quickly spreads, especially in areas with low humidity and dry conditions typical of wildfire-prone regions.

In contrast, heavy snowfall generally mitigates fire risk by saturating the ground and covering potential fuel sources with ice and snow. Earthquakes can occasionally lead to fires, primarily through damage to gas lines or electrical infrastructure, but they are not a direct cause of wildfires in the way human activities are. Excessive rainfall, while it may contribute to vegetation growth, can actually reduce the immediate wildfire risk by saturating the soil and increasing moisture levels in plants, making them less flammable. Therefore, the direct link between unattended cigarettes and campfires and the ignition of wildfires establishes the validity of this option as a leading causative factor.