What is a map projection and why is it hard to depict the earth on a flat surface accurately?

Humans have built artificial levees along the mississippi river to protect themselves and their property from floods. however, these structures also modify inland and coastal regions by disrupting the natural flow of sediment. artificial levees along the mississippi river a. reduce the amount of sediment deposited on floodplains and increase the amount of sediment deposited at the river's mouth. b. increase the amount of sediment deposited on floodplains and decrease the amount of sediment deposited at the river's mouth. c. increase the amount of sediment deposited on floodplains and at the river's mouth. d. decrease the amount of sediment deposited on floodplains and at the river's mouth.