Azoologist has been studying the annual migration of a species over a period of years. he missed the annual event on two occasions. at the end of six years, he submits his report, which includes the graph above. from his data, he concludes that the number of animals migrating is decreasing every year in a linear manner. what mistake has he made?

He has not accounted for the two years he missed.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.