Which of the following best describes the surface of Earth?

Most of the Earth surface, about 70%, is covered with water. Underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth's surface layer is made of rock. ... This outer layer formed a hard, rocky crust as lava cooled about 4.5 billion years ago.

Explanation:

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.