Ch 14 name two regions of the digestive tract where mechanical food breakdown occurs and explain

The answer is mouth and stomach. In the mouth, teeth are responsible for the mastication of the food into small particles before swallowing. In the stomach, the food is continuously churned by the stomach wall muscles as it mixes with enzymes and HCl hence breaking down the food both mechanically and chemically.

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.