Directions (66–85): record your answers in the spaces provided in your answer booklet. some questions
may require the use of the 2011 edition reference tables for physical setting/earth science
base your answers to questions 66 through 69 on the graph below and on your knowledge of earth science.
the graph shows changes in hours of daylight during the year at the latitudes of 0°, 30° n, 50° n and 60° n.

explain why all four latitudes have the same number of hours of daylight on march 20 and september 22.