The best answer to this question is:
C. A forest fire that was caused by lightning.
A forest fire could kill for example all the individuals of a certain species in a given area - this would be independent of the population density of the species. All the other factors would affect the population the more, the more dense it is.
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My guess would definitely be false, public transportation seems like a much more reliable mean.
D because it is freezing cold in Canada
