BROOKLYN - Fire crews are investigating the cause of an early morning fire in Bushwick.Police say a raging fire began on the third floor of a Furman Avenue apartment building early this morning, killing a 25-year-old woman.A woman who lives across the street says the flames shooting out of the building were so strong that the light from the fire actually woke her up. She says she saw dozens of residents rushing out of the building, which houses a funeral home on the first floor.The building owner says the third floor is completely gutted and that everyone who lives there has been evacuated.Firefighters say they had the blaze under control just before 5 a.m. and that no one else was injured.