While looking at a slide you observe an unknown crystal lying next to a red blood cell. The crystal is about 2.5 times the diameter of the red blood cell. What is the size of the crystal in um?

answer; the above answer to the above statement is (true)

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.