some physical regions of the united , canyons, desertsrocky mountainshigh, rugged mountain peaksinterior plainslowlands, fertile soilappalachian mountainslow, rounded mountain topshawaiian islandsrain forests, volcano topswhich of the following statements best describes the physical regions of the united states? a. their features are all similar. b. they all contain mountains. c. they are dominated by plains. d. features vary from region to region.