Australian AMC 2014 - Upper Primary Question 22

A plane was travelling at an altitude of 4500 metres for 20 minutes. It then climbed at a rate of 500 metres per minute for 5 minutes before descending at 350 metres per minute for 8 minutes. Which of the following graphs best describes the altitude of the plane over this time?

Graph labels: Time is the horizontal axis and Altitude the vertical axis.