What causes moon phases and what is it we see from Earth?

The phases of the Moon that we see are caused by the relative positions of the Sun, Moon and Earth. The phase of the Moon is defined by the proportion of the Moon lit up by the Sun that is visible from Earth.

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.

the missing space is phylum