The altitude of an airplane is represented in the graph below. A graph with time (minutes) on the x-axis and altitude (feet) on the y-axis. Points are at (0, 0), (20, 12,000), (40, 24,000), (60, 36,000), (80, 36,000), (100, 36,000), (120, 36,000), (130, 36,000), (140, 24,000), (160, 12,000), and (180, 0). Is the airplane’s altitude a function of time? Yes, because any input of time results in only one output of altitude. Yes, because the airplane increases and decreases in altitude at the same rate. No, because each output of altitude has more than one input of time. No, because the altitude is constant between 60 minutes and 130 minutes.