Are the black bears mammalsreptiles or amphibians?

Strictly speaking, "amphibian" refers to a distinct group of ectothermic invertebrates including frogs, toads, salamanders, and caecilians. For other things that equally well adapted to both land and water, the more appropriate adjective is "amphibious." Most members of the bear family are not any better adapted to water than humans are. A possible exception would be that of the polar bear, which regularly swim at 6 MPH (compared to 5 MPH as the world record for humans).