Which of these factors make hydrogen fuel cells a better option than burning fossil fuels? Hydrogen fuel cells have a higher energy efficiency. Hydrogen fuel cells create less pollution. Burning fossil fuels relies on outdated devices and technology. Hydrogen is the most abundant element in the universe. Hydrogen fuel cells are more expensive than fossil fuels.

im sorry i dont know

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.

a. spokes of a wheel.

as indicated in the question radial contains rad, also found in radius, so the fracture's would span the radius.