What primarily involves heat transfer by convection?

heating of solid from a liquid source

Explanation:

Convection heat transfer is the process of heat transfer in which a fluid is heated by a heat source that causes the fluid to rise up due to a change in its density. The convection current ensures that warmer and less dense fluid always rises up. The convection heat transfer may also occur in solids that are in contact with liquids.

what is the question?

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.