Answer:
c. pressure
d. temperature
Step-by-step explanation:
The Earth's layers all have different composition, and they all differ in the sense of being solid, or more liquid. There are two main factors that contribute to this, the pressure and the temperature. Both of these factors are able to change the condition of a material individually, but when they are combined than they have even greater influence. The crust is solid, and the main reason for that is that the pressure and temperature are relatively low. The mantle is consisted of molten rock because the temperature and pressure are higher. The outer core is liquid, as it has much higher pressure and temperatures even than the mantle. The inner core is the layer with the highest pressure and temperature, and they are so high that the material is actually solid because of it.