An engineering student is studying the effects of cryogenic treatments on a particular material. the treatment involves cooling the material with specific applications of liquid nitrogen. the temperature of the material in degrees celsius, y, can be modeled by the following graph, where x represents the time, in hours, since the treatment began. here are the answer choices: a.) the material's initial temperature is -30 degrees celsius. b,) the material's temperature reaches a maximum at 25 hours. c.) the material returned to its initial temperature after 40 hours. d.) the material's temperature reaches a minimum at 15 hours.