I think it is D because your responding to the cold from stimuli and by creating heat to keep your body the average temperature it is homeostasis.
At the base of the food chain
The answer is
B) Evolution
Adult Atlantic Salmon<span> live in coastal seas and </span>feed<span> on pelagic invertebrates ... The Atlantic </span>Salmon<span> is an iconic species in the north Atlantic </span>Ocean<span> and ... Unlike the pacific </span>salmons<span> (such as the Chinook</span>Salmon<span> [link]), Atlantic </span>Salmon do<span> not die after ... subpopulations that spawn in those rivers will almost certainly </span>go<span> extinct.</span>