Where on earth can you walk one mile south one mile east one mile north and end up where you started?

How am i supposed to know your lecture

Answer is b)eutrophication occurs when excess nutrients are present in aquatic ecosystems, resulting in the increased production of plant life and the subsequent decrease in the oxygen levels of the watereutrophication occurs when there are excess nutrients in a body of water. this results in plants having more food and reproducing  more, sometimes leading to more aquatic animal life as well. ultimately, this can reduce the oxygen level in the ecosystem. 

here is the correct answer.

i got it wrong but it showed me the correct answer.