The inca used to move supplies on difficult mountain terrain.
a.
camels
b.
horses
c.
llamas
d.
oxen

C. Llamas
They were very useful to their economy as they were the source of course wool and fuel (from their dung).

C.  llamas

Explanation:

The llamas are domesticated south Americana animals that are used for the meat and the pack animals by the Andean culture since the pre-Colombian era and are well socialized.  And have been found in the Incas culture as they switched from a hunter-gather lifestyle to an agricultural society. Essential animal to carry the load in the difficult terrines.

Mantle convection is the process that drives plate tectonics. the theory of plate tectonics states that the crust is divided into plates that float on the semi molten mantle below. the circular motion of the magma as it slowly rises and falls or move though convection cells drags the plates along causing them to move. the heat source in the lamp would represent the earth's core. the core is the source of energy that drives convection in the mantle. the lava represents molten magma under the earth's surface. if the lava lamp had floating pieces they would move as the circular motion of the lava in the lamp as it rises and falls would move them along the surface. these floating pieces would represent pieces of the earth's crust.