The region between the tip and the shaft of a long bone is the

The region between the tip and the shaft of a long bone is the metaphysis.

Explanation:

The metaphysis contains the growth plate, which is the part of the bone that grows during childhood. As it grows it starts to get harder along the tip and the shaft of the long bone.

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.