Final answer:
Big game mammals have experienced the most significant hunting rate decline over the past 50 years due to overhunting and resulting population decreases.
Step-by-step explanation:
Over the past 50 years in North America, among the groups of game species, it has been big game mammals (B) that have seen the most significant decline in hunting rates. This decline is largely attributed to overhunting, which has resulted in population decreases and, in some cases, local extinctions of large-bodied species. Over-hunting often results in faunal biomass collapses, a trend that has been documented worldwide. The depletion of big game populations leads to broader ecological consequences and shifts in hunting practices towards smaller, less vulnerable species.