Water is boiling on the stove. Can you explain what is happening in terms of particle energy, systems, and states of matter?

more energetic molecules change to a gas, spread out, and form bubbles. It requires energy to change from a liquid to a gas (vaporization). In addition, gas molecules leaving the liquid remove thermal energy from the liquid.

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.