The American Plains bison is a grassland species that eats mostly grasses. By the late 1800s, hunting came close to causing this animal to disappear from the western United States. In the early 1900s, landowners and the U. S. government took stepsto save the bison. The graph shows data collected in northern Yellowstone National Park between 1902 and 1915. A graph that plots 'Number of Bison' in the y-axis against 'Year' in the x-axis. The years mentioned in the graph are '1902', '1904', '1906', '1908', '1910', '1912', '1914', and '1916'. The numbers of bisons mentioned in the graph are '50', '100', '150', '200', '250', and '300'.

Which of the following events could have caused the change shown in the graph? Choose the two that apply.
A. natural disaster
B. decrease in food
C. increase in shelter
D. departure of bison
E. decrease in hunting