Explain in terms of Newton's first law why you should never step off a bus or train before
it has completely stopped.

Newton's 1st law demonstrates that unbalanced forces impact the motion of yourself when you get off the train. You would most likely lose your balance due to the difference in motion between the train and the ground.

Explanation:

Newton's first law states:

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.