Which of these graphs below illustrates water boiling in denver, colorado (altitude 1,600 meters.)

When water is boiling, this occurs at a constant temperature. Thus, in a temperature vs time graph, you would expect to find a flat horizontal line. So, the answer could either be A, B or C. Now, the normal boiling point at sea level is 100°C. However, since this is high above the sea level, the pressure is lower than normal. Consequently, the boiling point should be lower than 100°C. Thus, from the figure, the answer would be letter A.