On New Year's Day,thousands of Canadians Celebrate with a "Polar

On New Year's Day,thousands of Canadians celebrate with a "polar bear" swim.They jump into an ice-cold body of water at a lake or seaside.Needless to say,most people jump back out again within seconds as the water is shockingly cold at this time of year.Some peole elect to stay in the water longer,and notice that while the water remains cold,it feels less cold with the passage of time.What is this a result of

A)  adjusting just noticeable differences 
B)  sensory adaptation 
C)  perceptual assimilation 
D)  perceptual invariance