A. A plane takes off, gaining altitude at a constant rate. When it
reaches its cruising altitude, it remains there. The x-axis
represents time; the y-axis represents altitude.
B. A plane flies at a constant altitude before it begins its descent. It
then loses altitude at a constant rate. The x-axis represents time;
the y-axis represents altitude.
C. Before taking off, an airplane taxis around the airport. After
takeoff, the plane gains altitude at a constant rate. The x-axis
represents time; the y-axis represents altitude.
D. A plane takes off, gaining altitude at a constant rate. It then begins
its descent, losing altitude at a constant rate. The x-axis
represents time; the y-axis represents altitude.