Read the paragraph below. What is the main idea?

Wildfires caused by humans can happen because of arson, discarded cigarettes, and sparks from power equipment. When the conditions are right, wildfires can be caused by the fragments of hot rifle bullets. Wooded areas that have been cleared by logging are often covered by grasses that catch fire easily. By far, though, the majority of wildfires are caused by lightning strikes.
A) Human activity is the main cause of wildfires, though sometimes they begin naturally.
B) Lightning strikes only cause wildfires when humans are not able to prevent them.
C) There are several ways that humans can start wildfires, but most wildfires have natural causes.
D) Wildfires destroy animal homes as well as human homes, regardless of how they start.