Which of the following best describes the physical nature of the Earth's lithosphere and the asthenosphere?

A. Overall, both the lithosphere and the asthenosphere tend to flow and deform plastically.

B. The lithosphere is rigid and commonly deforms in a brittle manner; the asthenosphere tends to flow slowly and deform in a plastic manner.

C. The asthenosphere is rigid and commonly deforms in a brittle manner; the lithosphere tends to flow slowly and deform in a plastic manner.

D. Overall, both the lithosphere and the asthenosphere are rigid and brittle.