What does the law of the conservation of mass state

Does anyone have the answers to online physics course plato course physics, semester a v3.0

Scientists follow specific processes in order to determine valid explanations and conclusions from observations. david observed strange lights in the sky above his home outside of roswell, new mexico. the only explanation that makes sense to him is that there are ufos in the area. what should david do next to verify his explanation?

Notice how they put future which of the clouds shown would indicate a possible future rain storm? a) b) c) d)