Most U.S. beaches are shrinking or encroaching on the land rather than growing or moving seaward, so the land of the U.S. is getting smaller, not bigger. Causes include:单项选择题

Global sea level fell as the ice-age ice sheets grew, and this caused rivers to deliver much sediment to the coast.

Global sea level is rising, covering more land.

Global sea level fell as the ice-age ice sheets grew, exposing sand to the attack of large waves during winter storms, so beaches are now being removed.

Local regions are rising as fluid injection wells used for waste disposal bulge up the land in many places.

Dams on rivers have increased sediment delivery to the beaches.