The earth's layers can also be classified according to their rheology, based on their ability to deform and flow. This is especially important in the upper mantle when describing the relationship between the lithosphere and the asthenosphere. Which of the following is true regarding the lithosphere and asthenosphere?

a. The lithosphere is made of basalt and granite, while the asthenosphere is made of iron and nickel.
b. The asthenosphere flows because it is liquid.
c. The cool, brittle lithosphere floats atop the weak asthenosphere.
d. The lithosphere carries the higher-riding continental crust, while the asthenosphere carries the denser, heavier oceanic crust.

The lithosphere refers to the outer portion of the earth that cool and very rigid. It covers the crust and a very small portion of the upper mantle. It lies just above the asthenosphere layer. This layer is broken down into many small and large plates which are commonly known as tectonic plates.

The asthenosphere covers a portion of the asthenosphere and it supports the movement of lithospheric plates over it. This is possible because of its property that allows the rocks of lithosphere to float above it. The asthenosphere is comparatively weaker and though the rocks are solid in this region, but they tends to flow during the time of deformation.

Both these two layers plays an important role in the plate tectonic movement.

Thus, the correct answer is option (C).