How does a natural ""solar thermostat"" keeps the core fusion rate steady in the sun?

Explanation:

What is solar thermostat?

A solar thermostat automatically regulates temperature of the sun when the temperature reaches a certain point and its also known as gravitational equilibrium.

NOTE: if the core temperature decreases, then the fusion rate decreases and this lowers the pressure and the cause the core to contract and heat up.

Also, the increase in core temperature, increases the fusion rate and this raise the core pressure and this cause the core expands and cools down.

The fusion rate of the sun increase when core is a bit hotter. This increase in the rate of fusion produces more energy, which cause the core to expand slightly and cool.

The fusion rate is then slow down due to the cooling until the sun get back to it's original size and temperature. The fusion that occur in the sun concerts hydrogen into helium, energy and neutrinos.

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.