The best example of assuming causation is C) "Our town does not have a park where children can play. This explains why so many young people in our area are unhealthy."
In this statement, there is an assumption that the lack of a park directly causes the unhealthiness of the youth, which may not necessarily be true. There could be other contributing factors to the health of young people that are not considered here, making this a clear example of assuming causation without sufficient evidence.